Someone suggested a probably more understandable "minigame-only build plate" back.
I disagree.
For it is common knowledge that one can only create structures around energy-pylons, but minigame-only build plates would be cluttered and ineffective; One would have to explain what it is to every person that joins.
Acting on the general reaction that would make one assume that it is
not common knowledge that one can only create structures around energy-pylons, people who do not know such are likely not going to build anything of worth on your server. Instead they'll question petty things and end up going to a server with such names as "POLARSPARTAN's SNIPER CTF 50 POINTS = ADMIN".