Mempool terminology

Ancestor(s)

One or more "parent" transactions which must be confirmed before the current transaction.
The ancestor transaction(s) create outputs which are depended on by the current transaction.

Descendant(s)

One or more "child" transactions which must be confirmed after the current transaction.
The descendant transaction(s) depend on outputs from the current transaction.

Orphan

A transaction with missing ancestors.

When ancestor and descendant are encountered in the codebase, they refer specifically to other in-mempool transactions.

Ancestors and descendants can be confirmed in the same block but they must be in the correct order within the list of transactions for the block to be valid.