The short answer is that abstract is the opposite of concrete.
The long answer
Abstraction is basically a synonym for generalization. When we simplify something by throwing away irrelevant information, we are abstracting or generalizing. For example, a car is a more abstract concept than a Ford Mustang. When we refer to a Mustang as a car, we are generalizing the meaning of a Mustang. We are throwing away information about the object and arriving at a simpler concept, "car" in this case.
Consider the following scale:
Thing <-> Vehicle <-> Car <-> Ford Mustang <-> Shelby GT500KR
When we go to the right, we are becoming more concrete. When we go to the left, we are becoming more abstract. When we add detail, we are being more concrete. When we take away detail, we are being more abstract.
Something is said to be abstract if it is farther to the left in such a scale as something else.
Using the above scale, we could say that "vehicle" is abstract and "Shelby GT500KR" is concrete.
Abstract is a relative term like "tall" and "short". Nothing is tall or short, but only tall or short relative so something else. For example, is the Colosseum in Rome tall? It depends on the context. It is tall compared to a person, it is short compared to the Empire State Building or the CN Tower. When we say something is tall, there is always an implicit context since the word only makes sense relative to the context. We can say that the Colosseum is tall or short, depending if the context is people or buildings. When we say something is tall, we are saying it is tall relative to something else. Otherwise the concept "tall" has no meaning.
Likewise, when we say something is abstract, we are saying it is less concrete than something else. The word "abstract" has no meaning by itself.
Part of the confusion is that dictionaries often mix definitions with examples. So, its easy to confuse an example of abstract with its definition if you read a dictionary. Here are several definitions from the New Oxford American Dictionary:
- existing in thought or as an idea but not having a physical or concrete existence
- dealing with ideas rather than events
- make a written summary of (an article or book)
- an abstract work of art
These are all concrete examples of how the word "abstract" can be used, but they do not define it. These definitions won't help you understand what an Abstract Data Type is in computer science.
Here are some more definitions from the same dictionary:
- not based on a particular instance; theoretical
- denoting an idea, quality, or state rather than a concrete object
- extract or remove (something)
These definitions start to get at what the word actually means.
Meaning
See you in the funny paper[s] means "Goodbye, see you soon".
A Dictionary of Catch Phrases (1986) by Eric Partridge and Paul Beale says:
see you in the funny papers (—often and orig. I'll). 'This jocular farewell suggests that the person addressed is rather laughable: US: 1920s; extinct by the 1950s' (R.C., 1978). Perhaps adopted in the UK from American servicemen c. 1943. By c. 1955, (I'll) see you in the funnies.
Etymology
The OED has funny paper from 1874 and funny column from 1860, meaning "a (section of a) newspaper containing humorous matter or illustrations".
1920
The earliest example I found of the phrase is in a letter in Commercial Telegraphers' Journal (August 1920, Vol. XVIII, No. 8):

So long, boys, see you in the funny paper. "30."
J. N. HANNA,
Box 1004.
1921
Another in the Union Postal Clerk (March 1921, Vol. XCII, No. 3):
We will see you in the "funny paper" next month.
PRESS COMMITTEE.
1921
Here's a April 15, 1921 letter published in University of Virginia student paper The Virginia Reel (April 18, 1921 Vol. 1, No. 8):

Well, boys, must close now. La, la, till the next time, and I'll see you in the funny papers. Ever your, ADELAIDE.
1922
Here's a 1922 example in the signoff of a report in The Tusla Scout from Troop 12 by Ed M'Lain (published in The Tulsa Daily World, March 19, 1922):
Good-bye, see you in the funny paper.
This use by scouts suggests it's not insulting, but may be used in a good-natured, light-hearted mocking manner.
Best Answer
The phrase means that whatever it is engenders some strong emotion: here it will be laughter, but in other contexts it might be tears, surprise, or embarrassment.