Not held back, not kept under control. 'Restrain' means to hold something or someone back — so unrestrained is what happens when nothing is holding it. It is used most for feelings that pour out: unrestrained joy, unrestrained laughter, unrestrained anger, unrestrained grief. In these cases it is often admiring or at least sympathetic — unrestrained delight sounds wonderful, like a child who cannot stop laughing. It also describes growth or activity that nobody is limiting: unrestrained spending, unrestrained development, unrestrained capitalism, unrestrained use of power. Here the tone flips and becomes critical — the writer usually thinks somebody should have put limits on it. So the same word can praise or warn, and the noun beside it tells you which. There is a literal use as well: an unrestrained child in a car is one not in a seatbelt or car seat, and you meet this on safety notices and in accident reports. Note that unrestrained describes a lack of limits from outside OR from inside yourself — the joy nobody stopped, and the joy you did not try to hide.