Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo.
This is both grammatically correct and has meaning.
1. Buffalo, as in 'City of Buffalo, New York state'
2. buffalo, as in large herbivore aka bison, plural
3. buffalo, meaning to bully or intimidate.
A [Buffalo buffalo] B [Buffalo buffalo buffalo] C [buffalo Buffalo buffalo]
A: Bison that are from the city of Buffalo...
B: ...which are bullied by other bison from the city of Buffalo...
C: ...in turn bully other bison from the city of Buffalo.
It took me ages to understand this, because in normal speech you would include a link between A and B, like this:
Buffalo buffalo which Buffalo buffalo buffalo buffalo Buffalo buffalo.
...but actually there's no grammatical need for a 'which' or 'that' in that place.
My explanation uses the wikipedia entry, full version here: Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo - Wikipedia, the free encyclopedia
It's just a pity that the opportunity to legitimately use this sentence in conversation is never, ever going to arise.