A swim lane (or swimlane) is a visual element used in process flow diagrams, or flowcharts, that visually distinguishes responsibilities for sub-processes of a business process. Swim lanes may be arranged either horizontally or vertically. In the accompanying example, the swimlanes are named Customer, Sales, Contracts, Legal, and Fulfillment, and are arranged vertically.
Attributes of a swimlane 
The swim lane flowchart differs from other flowcharts in that processes and decisions are grouped visually by placing them in lanes. Parallel lines divide the chart into lanes, with one lane for each person, group or subprocess. Lanes are labelled to show how the chart is organized.
In the accompanying example, the vertical direction represents the sequence of events in the overall process, while the horizontal divisions depict what subprocess is performing that step. Arrows between the lanes represent how information or material is passed between the subprocesses.
Alternately, the flow can be rotated so that the sequence reads horizontally from left to right, with the roles involved being shown at the left edge. This can be easier to read and design, since computer screens are typically wider than they are tall, which gives an improved view of the flow.
Use of standard symbols enables clear linkage to be shown between related flow charts when charting flows with complex relationships.
When used to diagram a business process that involves more than one department, swimlanes often serve to clarify not only the steps and who is responsible for each one, but also how delays, mistakes or cheating are most likely to occur.
Many process modeling methodologies utilize the concept of swimlanes, as a mechanism to organize activities into separate visual categories in order to illustrate different functional capabilities or responsibilities (organisational roles). Swimlanes are used in Business Process Modeling Notation (BPMN) and Unified Modeling Language activity diagram modeling methodologies.
Alternate terms 
A swim lane may also be referred to as a functional band (as it is in Visio 2007) and is used in the same way, to create a cross functional flowchart to map a process within the functional units of a business. The term functional band precedes the use of swimlane and is seemingly in decline as the preferred term.
The origin of the term swim lane is not clear. One possibility is as part of the JBoss jBPM jPDL (Process Definition Language) graphical process designer a part of the JBoss jBPM framework for process languages.