Merge types in the Source Code Management ( few merge types in the Azure DevOps services ).

There are four types of the merge types:

1. Merge ( no fast forward ) : Non-linear history preserving all commits.

2. Squash merge ( commit ) : Linear history with only a single commit on the target.

3. Rebase and fast-forward : Rebase source commits onto target and fast-forward.

4.  Semi-linear merge : Rebase source commits onto targets and create  a two-parent merge.