What’s the difference between sperm and semen? And can pre-ejaculate get you pregnant?

Semen, sperm, spunk, cum, ejaculate, pre-cum, seminal fluid. These are just some of the many words we use to describe what comes out of an erect penis.
Some of these terms can be used interchangeably, but they’re not all the same. Do you know the difference?
What is sperm?
Sperm are male reproductive (sex) cells. The word...