To merge is to combine changes from one Git branch with another. It is like bringing two sets of recipe edits together into one shared version.
When a feature is ready, its branch may be merged into the main branch. If both branches changed the same lines in different ways, Git may ask a person to choose how those changes should fit together.
Reviewing the combined result is important. A successful merge means Git could combine the files; it does not guarantee the app behaves as intended.