What is it

Pointer that points to the commit from which the working tree's current state was initialized.

• Could be wherever you are in the commit history.

Head References

HEAD~2 # 2 commits older than HEAD
HEAD^2 # second parent of HEAD when HEAD was a merge, otherwise illegal
HEAD@{2} # 3rd from list in git reflog
HEAD~~ # 2 commits older than HEAD
HEAD^^ # 2 commits older than HEAD

# 0th = HEAD
HEAD~0 # same as HEAD
HEAD^0 # same as HEAD

# Shorthand
HEAD~ # shorthand for HEAD~1