"Somebody Else's Problem", an effectively-magical field that obscures things you think aren't relevant to you, such that even though you see them (or hear them or read them) you don't actually *notice*, and quickly forget.
More generally, the phenomenon that causes people to ignore issues that they know about but think of as either not something they can do anything about, or not personally relevant to them right now. This can result in something that's very important to a group of people being ignored by every individual member of that group.
Popularized by Douglas Adams in the "Hitchhikers Guide to the Galaxy" series, in which Ford Prefect describes it as:
"An SEP is something we can't see, or don't see, or our brain doesn't let us see, because we think that it's somebody else's problem.... The brain just edits it out, it's like a blind spot. If you look at it directly you won't see it unless you know precisely what it is. Your only hope is to catch it by surprise out of the corner of your eye."
In that series, a strange object can be effectively hidden from view while out in plain sight, by an "SEP field", which "relies on people's natural predisposition not to see anything they don't want to, weren't expecting, or can't explain."
It's just been sitting there all day, hundreds of people have walked by, and nobody said anything or even turned to look! It's like it's got an SEP field around it.
when your out eating with friends or doing any activity costing money, paying separately or individually; not paying together.
waiter: "can i ring you guys up?"
group: "yes, but we'd like to pay seps if possible"
Arthur looked dilligently across the cricket field. Just then, it was there. Ford jumped in mid-air. "THERE IT IS, ARTHUR!! the S.E.P.!!"
Someone Elses Problem
The customer won't fix that part of the car, now it's S E P.
The nickname for a person named "Septimus"
Jenna: Sep, wanna go to the tower?
Septimus: i wish i could but i got an exam i have to study for.
Your website is offline? Sorry, that's an SEP.
Retarded way of saying sup
White person to black person: Sep my nigga?
Black Person: *Death eyes*
White Person:*Bolts for his life*