What is an obstacle?
FAR 91.119(b) requires an altitude of 1000' above any obstacle within a 2000' horizontal distance from the plane when over congested areas.  So what is the definition of an obstacle?  Is it anything over 50' height?  Anything above ground such as a house or even a fence?  I don't know if it was from the FAA or NTSB but I think I saw a definition that included anything man made or natural.  That could include a tree, bush or ground higher than the surrounding terrain.
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Consider it anything which might scratch the paint on your airplane, which would include all the things you mentioned.
Thanks, but I'm looking for a legal definition with references if possible.


That covers the structures side.  In addition, the DDOF referred to there also refers to "tree" and "vegetation" obstacles. Various FAA publications cover "terrain obstacles", covering the "higher terrain" portion of your question.  Does that help?
How does this sentence enter into the issue.  From the link you sent:

"Please note that some of these categories differ from obstacle types used by FAA's regulatory specialists."

I think your link was for charting purposes, not enforcement actions for FAR 91.119(b), maybe.

I think NTSB board case precedent might be the place to look.
Here's where to look for NTSB cases:


You can also search for official legal interpretations of that regulation here:


Beyond that, I suggest you direct your question in writing here:

Office of the Chief Counsel (AGC-200)
800 Independence Avenue SW
Washington, DC 20591
I found several references to what defines a congested area but none about the definition of obstacle.  Will keep looking.