Depending who you ask, definitions may vary and cancel each other out (in some ways).
To some, jungle is an earlier form of drum-'n'-bass that evolved gradually out of hardcore upping the BPMs and breakbeats in the early-mid 90s. To others, jungle is a "rougher, raw" type of drum-'n'-bass, hence the name "jungle" which could be part of "urban jungle", or rough life in the city (as featured in Goldie's "Inner City Life"). Some avoid the term as they believe it is racist, i.e. as in "jungle bunny" referring to Euro black people making their urban music like how it is paralleled in the States as hip-hop/rap culture.
For what it's worth, the allmusic.com definition (worth checking out but can't be linked to) combines both of them under the same heading. I believe the overlap is pretty big anyway and not worth quibbling about.
Hope this helps 
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