git merge <branchname>
Integrates changes from the specified branch into the current branch.
This command is essential for combining different lines of development by merging a separated branch into your current branch in order to integrate changes from parallel efforts.
It operates by analyzing the commit histories to determine whether a fast-forward merge is possible or if a three-way merge is required, and it can be refined using options such as --no-ff to always create a merge commit or --squash to condense all changes into one commit.
Other closely related commands include git rebase, which offers an alternative linear history integration, as well as variants like git merge --abort to cancel an ongoing merge, all of which provide additional controls to manage branch integration workflows.