Web conferencing refers to a service that allows conferencing events to be shared with remote locations. These are sometimes referred to as webinars or, for interactive conferences, online workshops. In general the service is made possible by Internet technologies, particularly on TCP/IP connections. The service allows real-time point-to-point communications as well as multicast communications from one sender to many receivers. It offers information of text-based messages, voice and video chat to be shared simultaneously, across geographically dispersed locations. Applications for web conferencing include meetings, training events, lectures, or short presentations from any computer.
Some web conferencing solutions require additional software to be installed (usually via download) by the presenter and participants, while others eliminate this step by providing physical hardware or an appliance. In general, system requirements depend on the vendor. Some web conferencing services vendors provide a complete solution while others enhance existing technologies. Most also provide a means of interfacing with email and calendaring clients in order that customers can plan an event and share information about it, in advance. A participant can be either an individual person or a group. System requirements that allow individuals within a group to participate as individuals (e.g. when an audience participant asks a question) depend on the size of the group. Handling such requirements is often the responsibility of the group. Most vendors also provide either a recorded copy of an event, or a means for a subscriber to record an event. Support for planning a shared event is typically integrated with calendar and email applications. The method of controlling access to an event is provided by the vendor. Additional value-added features are included as desired by vendors who provide them. Besides exceptions (e.g. Openmeetings, TokBox, WebHuddle, BigBlueButton), web conferencing services do not apply free software but proprietary software, see Comparison of web conferencing software.
The term "webinar" is a portmanteau of web and seminar, meaning a presentation, lecture, or workshop that is transmitted over the Web. Some argue that webinars might be one-way, from the speaker to the audience with limited audience interaction, so one-way broadcasts are perhaps more accurately called webcasts. Webinars themselves may be more collaborative and include polling and question & answer sessions to allow full participation between the audience and the presenter. In some cases, the presenter may speak over a standard telephone line, while pointing out information being presented onscreen, and the audience can respond over their own telephones or microphones connected to their computers, speaker phones allowing the greatest comfort and convenience. There are web conferencing technologies on the market that have incorporated the use of VoIP (voice over Internet protocol) audio technology, to allow for a completely web-based communication. Depending upon the provider, webinars may provide hidden or anonymous participant functionality, making participants unaware of other participants in the same meeting.
Interactive conferencing 
For interactive "online workshops" web conferences are complemented by electronic meeting systems (EMS) which provide a range of online facilitation tools such as brainstorming and categorization, a range of voting methods or structured discussions, typically with optional anonymity. Typically, EMS do not provide core web conferencing functionality such as screen sharing or voice conferencing though some EMS can control web conferencing sessions.
Other typical features of a web conference include:
- Slide show presentations - where images are presented to the audience and markup tools and a remote mouse pointer are used to engage the audience while the presenter discusses slide content.
- Live or Streaming video - where full motion webcam, digital video camera or multi-media files are pushed to the audience.
- VoIP (Real time audio communication through the computer via use of headphones and speakers)
- Web tours - where URLs, data from forms, cookies, scripts and session data can be pushed to other participants enabling them to be pushed though web based logons, clicks, etc. This type of feature works well when demonstrating websites where users themselves can also participate.
- Meeting Recording - where presentation activity is recorded on the client side or server side for later viewing and/or distribution.
- Whiteboard with annotation (allowing the presenter and/or attendees to highlight or mark items on the slide presentation. Or, simply make notes on a blank whiteboard.)
- Text chat - For live question and answer sessions, limited to the people connected to the meeting. Text chat may be public (echoed to all participants) or private (between 2 participants).
- Polls and surveys (allows the presenter to conduct questions with multiple choice answers directed to the audience)
- Screen sharing/desktop sharing/application sharing (where participants can view anything the presenter currently has shown on their screen. Some screen sharing applications allow for remote desktop control, allowing participants to manipulate the presenters screen, although this is not widely used.)
Web conferencing is often sold as a service, hosted on a web server controlled by the vendor. Offerings vary per vendor but most hosted services provide a cost per user per minute model, a monthly flat fee model and a seat model. Some vendors also provide a server side solution which allows the customer to host their own web conferencing service on their own servers. Examples of this include Microsoft Office Communications Server (Lync Server).
Web conferencing technologies are not standardized, which has been a significant factor in the lack of interoperability, transparency, platform dependence, security issues, cost and market segmentation. In 2003, the IETF established a working group to establish a standard for web conferencing, called "Centralized Conferencing (xcon)". The planned deliverables of xcon include:
- A basic floor control protocol. Binary Floor Control Protocol (BFCP) published as RFC 4582
- A mechanism for membership and authorization control
- A mechanism to manipulate and describe media "mixing" or "topology" for multiple media types (audio, video, text)
- A mechanism for notification of conference related events/changes (for example a floor change)
Deployment models 
Web conferencing is available with three models: hosting service, software and appliance.
An appliance, unlike the online hosted solution, it is offered as hardware. It is also known as "in-house" or "on-premise" web conferencing. It is used to conduct live meetings, remote training, or presentations via the Internet.
Real-time text chat facilities such as IRC appeared in the late 1980s. Web-based chat and instant messaging software appeared in the mid-1990s. In the late 1990s, the first true web conferencing capability became available from Starlight Networks  StarLive product  and dozens of other web conferencing venues, most notably WebEx followed thereafter.
Web conferencing started with Plato, a small standalone system that supports a single class of terminals connected to a central computer.
Software and service providers 
Notable vendors with articles:
- ACT Conferencing
- Adobe Acrobat Connect
- Blackboard Inc.: owner of Elluminate, Wimba
- Cisco WebEx
- Citrix Online: owner of Netviewer, GoToMeeting, GoToWebinar
- Dimdim closed to new registration as of January 6, 2011
- Epiphan Systems
- Fuze Meeting
- Genesys Meeting Center
- Google Wave suspended as of August 4, 2010
- IBM Lotus Sametime and IBM LotusLive
- Microsoft Office Live Meeting
- OmNovia Technologies
- Oracle Beehive
- RHUB Communications Inc.
- Saba Meeting: previously known as Centra
- Starlight Networks StarLive
- WebTrain not active
See also 
- Comparison of web conferencing software
- Collaborative software
- Electronic meeting system
- Hybrid event
- Web television
- "Cost-effective Solution for Video Conferencing". Retrieved 2011-07-04.
- "Webinar Definition". PC Magazine Encyclopedia. Retrieved 2008-06-29.
- "Exceptional Webinars Made Easy". EIC Inc.
- World Web Event Services Markets - N100-64, Frost and Sullivan, page 10, 2006, "The main features within the web event services market"
- Centralized Conferencing (xcon)
- "Binary Floor Control Protocol". Internet Society IETF. November 2006.
- "Online broadcasting".
- "Apps for Streaming Servers".
- "Trademark Assignment for Webinar". United States Patent and Trademark Office. February 6, 2003. Retrieved 2008-06-29.
- "History of Web Conferencing".
- Web-Conferencing Software Tools – A Market Survey from the University of St. Gallen, Switzerland
- Ease of Use in Web Conferencing – Why it Matters from Wainhouse Research
- Webinar Software Providers
- Critical Factors for Adoption of Collaboration Technologies in the Enterprise from Collaborative Strategies