WIP (work-in-process) defines all the work and resources needed to build the functionality of a project. In software development, WIP includes documentation, code, tests, results, etc. All of these are WIP until the project deployment in production.
WIP limits in Kanban and Scrumban methodology means dividing the whole amount of work into smaller tasks to make blockers and bottlenecks visible. It helps to foresee and resolve them sooner and to continue the workflow.