x1 is a commit of x2 about x3 in x4; x1=p1=v1=s1 is a snapshot / record / commit / revision / immutable tag / versioned reference / document / sub-hierarchy of data x2=v2, about / pertaining to x3=v3, in repository / data storage / medium (especially of a hierarchy / graph of immutable data / snapshots) x4=p2=v4, immutable and static / unchanging in property x5=s2 (can vary in precision and degree of immutability) in response to stimulus / conditions x6=s3.
If in the context of VCS, this can be used to refer to e.g. git commits or darcs patches / snapshots.