Chording means pushing several keys or buttons simultaneously to achieve a result.
In music, more than one key are pressed at a time to achieve more complex sounds, or chords.
Mouse chording allows a user to use a two-button mouse, trackball, or touchpad as if it where a three-button device. For example, in the Unix graphical user interface (known as X11), the middle button is used to paste text. Since Microsoft-type mice traditionally only had two buttons, users of Unix-type systems such as Linux and BSD chord the right and left buttons to paste text.
TipTapSpeech an application for the iPhone and iPad is a chord-based text entry solution for touch screen computing.
A GKOS chording keyboard application development for iPhone was started on the GKOS Google Group  on May 25, 2009. The application for iPhone became available on May 8, 2010, and a similar application for Android on October 3, 2010. Thumbs are used to press the keys that are located towards the sides of the screen, either a single key or two keys simultaneously. - The further development of GKOS has led to the ComboKey keyboard that works better on smartphones. ComboKey also allows one-hand typing with the hand holding the device, generating combinations by occasional swipes to other keys.