Wood is the material which forms the trunks and branches of trees.

A wood is a fairly large area of trees growing near each other. You can refer to one or several of these areas as woods, and this is the usual form in American English.

If something or someone is not out of the woods yet, they are still having difficulties or problems.

You can say 'touch wood' in British English, or 'knock on wood' in American English, to indicate that you hope to have good luck in something you are doing, usually after saying that you have been lucky with it so far.