Work Stages can be used to indicate the status of a Project, Item, Quote, or Invoice.

Work Stages are grouped by work state ie "Active Stages", "Completed Stages", and "Deleted Stages", which represent key phases in a project or task's lifecycle. Work states can have multiple stages, which represent the steps that need to be completed before moving onto the next phase. As, for example, the below image where the "Active Stages" include "In Progress", "On Hold", and "Pending":

Changing the Work Stage on any particular Project/Item/Quote/Invoice from one set of work state to another not only has a labelling affect, but also changes the state of that particular piece of work, ie changing the Work Stage on a Project from an "Active" stage to a "Deleted" stage would delete the Project.

You can add a Work Stage by clicking the "+" symbol underneath a work state group:

Hovering over an existing Work Stage will provide you with the options to delete a Work Stage, or change the color associated to the Work Stage: