When someone writes "nit: removed whitespace" on a commit, what does "nit" mean? I've also seen it capitalized as if it were an abbreviation (i.e. NIT). For an example usage see this post:
Of course there is a difference between a comment saying: "Nit: Trailing whitespace" and "According to Section V, Subsection VII of the Coding Manual you should never add trailing whitespace. Please see that you don't." or some stuff like that. The latter is a passive-aggressive potshot, the former IMO is just a quick reminder.
Other example from "Chromium Code Reviews":
Issue 9662: fix minor style nit (Closed)
EDIT: And an answer comes from Bugzilla's review page:
Sometimes the reviewer will prefix his comments with "Nit:". This means that he's just "nitpicking"--you don't have to fix these points, but we'd like you to.