WASHINGTON — Counterintelligence investigation. Wiretapping. Unauthorized disclosures of classified national security secrets.

Those phrases punctuated congressional testimony on Monday when the F.B.I. director, James B. Comey, said for the first time publicly that the bureau was conducting a counterintelligence investigation into whether members of the Trump presidential campaign worked with Russia to influence the 2016 election. Mr. Comey’s comments introduced many concepts that most people rarely hear.

The intelligence community has concluded that the Russian government employed a variety of tactics — including the hacking and release of Democrats’ emails — to sway the election against Hillary Clinton.

Here are some answers to questions that came out of Mr. Comey’s testimony:

What is a counterintelligence investigation?

Unlike a typical criminal investigation into organized crime or drug trafficking, a counterintelligence case is not typically focused on prosecuting someone. It is more spycraft than law enforcement. Every day, teams of F.B.I. agents listen to wiretaps on foreign officials and conduct surveillance on people suspected of being foreign agents in cities around the country. But once they know someone is a spy, they do not necessarily swoop in with handcuffs. In the counterintelligence world, it is often most valuable to watch these people — maybe for years — and learn whom they talk to, what their mission is and how they operate.