A task force is, essentially, a non-independent subgroup of a larger WikiProject that covers some defined part of the WikiProject's scope. For example, the United States military history task force of the Military history WikiProject deals with the military history of that specific country; and the Nintendo task force of the Video games WikiProject covers a particular game creator.
The distinction between a task force and a WikiProject is that the task force minimizes bureaucratic overhead: It relies on the parent project to provide much of the procedural and technical infrastructure. A task force, for example, uses the core project's peer-review and assessment processes rather than creating its own, thereby allowing it to focus on writing and editing.
A task force is generally set up on a subpage of the parent project page. In cases where the task force is a child of two projects (in other words, where its scope is the intersection of that of its two parents), the subpage can be arbitrarily placed under either of the projects, and a redirect can be created from the equivalent subpage in the other; see, for example, the Korean military history task force, run jointly by the Military history and Korea WikiProjects. The task force page can take any form, but should be initially constructed with minimal bureaucratic fluff. Projects with large numbers of task forces will often adopt a more-or-less standard layout for all of them, perhaps including common technical features; for example, each of the task forces of the Military history WikiProject has a standardized template for listing open tasks.
Task forces will generally not have their own talk page banners; instead, they are integrated directly into the parent project's banner via an optional parameter. For example, {{WPMILHIST}} includes a large number of task force parameters. It is possible to use this integration to automatically generate assessment data for a task force based on the assessments entered for the main project; this ensures that task forces don't need to conduct assessments independently.