I see in some books the authors call a one dimensional linear system a pencil, but in other books one call a linear system $|D|$ is not compsited with a pencil if $\dim \phi_{|D|}(X)\geq 2$ and even someone just say a pencil of curves etc. It seems these terms have different meanings. My question is the following.

What is the common pointview about the notion of a pencil? What is the realtions among above terms?