Something based on experience; a guess based on what you know.
Planet X was a theoretical planet that scientists thought existed. They mistook from a miscalculation in Neptune's mass.
by mr.mcswagsalot December 13, 2016
A person who is a hardcore canadian. Typically says "eh" at the end of every sentence. Yet can kick ass when bitched at and are mainly potheads. Will junk punch whoever pisses them off then yell you know whyyyyy
Blake: Dude DJ was a total theoret yesterday.

Justin:Really?

Blake: Yeah! That dude didn't even know what came to him.
by Justin1369 December 21, 2008
It means that something could possibly happen. It is highly unlikely it will ever happen, but there is a chance it could happen.
1. Obama can theoretically never be a good president.

2. Theoretically the Illuminati are real.

3. Theoretically it could happen.
by The Inprectichous Man January 31, 2015
When you discover that your code is not giving the right results, not because there is any bug in your program, but because there is a bug in the theory on which it is based.

Theoretical bugs are rare but more common than thought. When you find one, your perception of the world improves quantically.

A more day to day example, it is when you realize something you never saw before, not because it was not there, but because your mental model of the world didn't include it.
case 1
JC: I've been trying to find the bug in this program all night, but its looks perfect. Don't know why sometimes is producing weird results.
Guru: Its time to chase some Theoretical bugs.

case 2:

Linux_user: The problem with microsoft is not that they produced bad programs, but they copypasted so much software from other people, that the outcome was a walking Theoretical bug. At some much extent that, when it crashed it means it was really working.
by jcmid February 4, 2010
Old friends that you never really hear from anymore, apart from the occasional Text msg, Email or fleeting birthday card, that always contains one of the phrases: "we should meet up, hang out, do something, I'll call you..." but never actually make any arrangements. These are good on paper mates, those that bump up your personal sense of popularity but never actually see. Friends in theory.
"Are you kidding, Annie's not going to come, she's a Theoretical Friend..."
by KimberleyStrange January 31, 2006
A woman of cougar age (usually divorced, separated or unmarried). She doesn't hunt younger men. Instead she lusts at them and mentions it to her close friends and/or relatives in private.
Mom (in a whisper): "Meredith, you see those 5 guys over there? They're hot! Aren't they?"

Meredith: "OMG Mom!!! Those guys are all my age!!!"

Mom (still whispering): "Yeah, I know. But I'd love to get with one of 'em. Too bad I could never tell them that."

Meredith: "You're such a theoretical cougar"
by blacksburgcougee June 4, 2011
A person who likes everybody but can;t get a single one.
"Yo, you see that ugly girl over there? She's a theoretical whore."
by FatGutOmega March 13, 2009