'“In a project's outline, a mechanism to show normal tasks beneath their summary tasks, to see more levels of detail. Usually achieved using the Show Subtasks button. Can also be used to expand by group and to show assignment detail (on task usage and resource usage views). See also collapsing.

'SOURCE; microsoft project glossary-projectlearning.net

In an outline, making visible the collapsed tasks that are immediately subordinate to summary tasks.

SOURCE: apm.org”