How long is a term for a U.S. senator?

What does this answer mean?

A U.S. senator serves a six-year term. Article I, Section 3 of the Constitution set the six-year term, and the 17th Amendment kept it when it changed how senators are elected.

Senate elections are staggered. The Constitution divided the first senators into three groups, so about one-third of the Senate is up for election every two years. That means the whole Senate never changes at once, which makes it steadier than the House, where every seat is elected every two years.

The Constitution doesn't limit how many terms a senator can serve, so a senator can be re-elected again and again. To serve, a senator must be at least 30 years old, a U.S. citizen for at least nine years, and a resident of the state they represent.

Don't mix this up with the other terms: representatives serve two years, and the president serves four. At the interview, say "six years."