My answer will be fast and loose, but I don't mean to be obtuse.
I have a definition, but I'm not literally defined.
You have a meaning within geometry, but literally you're just space.
The simplest of shapes: circles and lines.
Angles are commonly drawn with circles and lines, like with radians.
A decimal you'll require;
The measurement of an angle doesn't usually require a decimal, but most numbers innately have them...? An angle does require a point, though.
my anagram leads a choir
Anagram of angle is angel, which can lead a group of them called a choir.