Full Idea
To idealize is to trade accuracy in describing the actual for simplicity of description, and the compromise can sometimes be struck in different ways.
Gist of Idea
Idealisation trades off accuracy for simplicity, in varying degrees
Source
Philip Kitcher (The Nature of Mathematical Knowledge [1984], 06.5)
Book Reference
Kitcher,Philip: 'The Nature of Mathematical Knowledge' [OUP 1984], p.144
A Reaction
There is clearly rather more to idealisation than mere simplicity. A matchstick man is not an ideal man.