In classifying 1 manifolds one has the following lemma
Let $f:I \rightarrow M $ and $g: J \rightarrow M$ be parametrizations by arc-length. Then $f(I) \cap g(J) $ has at most two components.
What does components mean here?
Also, I am reading Milnor's Topology from the differentiable viewpoint. He uses many concepts without defining and the reader is expected to know them already. Which is a good reference wherein I can find most of them?