https://www.atlassian.com/git/tutorials/refs-and-the-reflog/the-reflog


You can also refer to commits relative to another commit.
The ~ character lets you reach parent commits.

For example, the following displays the grandparent of HEAD:

git show HEAD~2

But, when working with merge commits, things get a little more complicated.
Since merge commits have more than one parent, there is more than one path that you can follow.
For 3-way merges, the first parent is from the branch that you were on when you performed the merge,
and the second parent is from the branch that you passed to the git merge command.

The ~ character will always follow the first parent of a merge commit.
If you want to follow a different parent, you need to specify which one with the ^ character.

For example, if HEAD is a merge commit, the following returns the second parent of HEAD.

git show HEAD^2

You can use more than one ^ character to move more than one generation.
For instance, this displays the grandparent of HEAD (assuming it’s a merge commit) that rests on the second parent.

git show HEAD^2^1

To clarify how ~ and ^ work, the following figure shows you how to reach any commit from A using relative references.
In some cases, there are multiple ways to reach a commit.

              A^2-1
              A^2^1  A^2

             -- O --- O --
            /             \
  O ---- O ---- O ----------- O

 A-3    A-2    A-1            A
A^2-3  A^2-2   A^1

Relative refs can be used with the same commands that a normal ref can be used.
For example, all of the following commands use a relative reference:

# Only list commits that are parent of the second parent of a merge commit
git log HEAD^2

# Remove the last 3 commits from the current branch
git reset HEAD~3

# Interactively rebase the last 3 commits on the current branch
git rebase -i HEAD~3