An ordinary commit, however, has exactly one parent.
An initial commit (root commit) has no parents.
A commit that was created as part of a merge has multiple parents: one for each line of history.
Looking at the content of a commit object
git cat-file commit 5f39acdb8
git cat-file commit HEAD
To commit
«to commit» (the verb rather than the noun) describes the action of storing a new snapshot of files into the Git history: it creates a new commit object representing the current state of the index and advances the HEAD to point at the new commit.
The commit objects form a directed acyclic graph because they have parents (which makes them directed) and there is no chain which begins and ends with the same object (which would make them acyclic).