What is Section 702 of FISA, anyway?

In The News Piece in CNN
Jan. 11, 2018

Joshua Geltzer was quoted on CNN about Section 702 of FISA:

What exactly does that mean, and does 702 allow the surveillance of American citizens, even incidentally? Here are some of the answers, including analysis from Joshua Geltzer, the former senior director for counter-terrorism at the National Security Council and current executive director of the Institute for Constitutional Advocacy and Protection at Georgetown University Law Center.
What is FISA Section 702?
It's just one part of the Foreign Intelligence Surveillance Act. The section specifically "allows the government to obtain the communications of foreigners outside the United States, including foreign terrorist threats," as laid out in the House Intelligence Committee FAQ sheet. For example, the program allows the government to obtain the emails or phone calls, without a warrant, of a non-American ISIS member who is outside the United States and might be plotting an attack. The committee FAQ points out that Section 702 does not allow the government to target the communications of any American, even if that American is a terrorist.