"Lightly" Edited?
Not quite to make of the autism comment, but anyway...
Lightly edited is if you modify the spacing, non-alphabetical characters and also change the upper/lower case lettering.
Punctuation tweaked is nearly the same, but only allows a limited set of non-alphabetical characters to be modified as well as case.
There's also "updated" if you don't change any text in the message (change the subject, group etc, or just don't change a thing but update anyway!).
Theoretically there's also an "added to" message, but I think this always comes up as "edited" due to annoying reasons I won't blab on about.
All there to give the GM a rough idea of how much information was changed in a post.