jello can refer to different things:
Jell-O
A colloquial way of saying Hello
Jello Biafra
Green Jello, the comedy heavy metal band (sued and later changed name to Green Jellÿ)
The Jell-O Belt, a colloquial geographical term in American English that references a clichéd Mormon overfondness for Jell-O.
Jello, a military slang term for a plan or operation that is not solidified, where details are uncertain, and/or not yet known, at present. See also 'indecisive.'