WiP Limit is part of the the set of rules for Kanban-projects (Kanban is a project management method or system of continuous improvement). WIP stands for Work-in-Progress, i.e. tasks in progress (in contrast to completed or not started tasks).
For each process step (for example: analysis, development, testing) a limit is set for the number of tasks that can be processed simultaneously. A WiP limit of "3" for the process step "development" (compare Kanban Board) means that a maximum of 3 tasks may be processed in parallel by the developer(s) working in a Kanban team. On a Kanban board, a maximum of 3 index cars in the column "Development" will be admitted.
This WiP limit avoids task switching (which causes inefficiencies). WiP limit is supposed to ensure higher quality of the results, since constant task switching can lead to unfocused work. Likewise, the lead time of tickets (tasks) is increased, i.e. tasks that are fed into the editing process can be completed within a shorter time; the predictability/deadline adherence of the process is thus increased, too.