What is a commit from Git's perspective?

A commit is a Git object that contains:

• a reference to the tree (the project's file structure);
• a reference(s) to the parent commit (one or more);
• the author and committer;
• the date and time;
• the commit message;
• a cryptographic hash (SHA-1 / SHA-256).

#What "snapshot" means

• each commit captures the full state of the project;
• unchanged files are reused by reference, not copied;
• commits form a directed acyclic graph (DAG).

#Why a commit cannot be changed

• a commit's hash is computed from its content;
• any change -> a new hash -> a new commit;
• this guarantees the integrity of the history.

#How Git uses commits

• a branch is a pointer to the latest commit;
• HEAD points to the current commit;
• a merge is a commit with multiple parents.

#Short version for an interview

A commit is an immutable Git object that contains a snapshot of the project and references to previous commits.