This is a colloquial version of the word "probably", in common usage in the upper Midwest, especially those areas of Wisconsin whose populations were drawn from German-speaking immigrants like Milwaukee and Madison. Definitely predates Internet.
Shortened version of "probably". Typically used in online conversations, although REALLY lazypeople have started using it in verbal conversations as well...
A spoken colloquialism that existed pre-internet, despite what many people claim.
"Prolly" is a clipped pronunciation of "probably"; compare with "g'day" as a clipped pronunciation of "good day", or "gonna" as a common spoken shortening of "going to".
Certainly non-standard, but not necessarily indicative of the writer's laziness. For some, writing in this manner mimics their natural speech pattern/dialect.
She said she'd prolly come over after she's finished relaxin' at the beach.
(spoken example) "I'm prolly gonna head down to Toranna {Toronto} for the May 2-4."
Literary colloquialism for "probably", most likely first used in print in John Kennedy Toole's Confederacy of Dunces, (1980), in the speech of one of the book's characters, the mother of the protagonist, Ignatius J. Reilly. The use of the word is meant to reflect the speech typical of white working-class residents of New Orleans, Louisiana.
Obviously a shortened word for 'probably' now used in internet conversations. Before the advent of this usage, it was commonly used in southern U.S. states in particular Texas as common vernacular and does NOT indicate laziness but dialectal and regional verbage.
Using 'prolly' is not a sign of idiocy or laziness but apropos savoir faire, subcultural quirks, accents and mannerisms just like many other phrases that come out of regional places.
Just think Pigeon English in Hawaii, Brooklyn slang or English/British expressions....we all got 'em!
Y'all prolly think I'm dumb for using this but it ain't so. I just wanna get to the point faster without havin' ta use so many goddamnletters! ;D