The term “obstruction of justice” has been swirling inside Washington D.C. and across cable television ever since President Donald Trump fired FBI Director James Comey last week. The talk only intensified after the New York Times cited a memo from Comey claiming Trump had asked him to shut down an investigation into former National Security Adviser Michael Flynn following his resignation.

“Lots of chatter from Ds and Rs about the exact definition of “obstruction of justice,” Senator Chris Murphy tweeted Tuesday with a link to the Times report.

Yesterday, secrets to the Russians. Today, obstruction of justice? When does this end?” Senator Sheldon Whitehouse tweeted.

But what exactly is obstruction of Justice and how does it relate to the headlines that have been coming out of the Beltway?

Obstruction of Justice is essentially someone who intentionally intervenes or tampers with an ongoing investigation.

“You can’t get in the way or do anything to impede an investigation that has already been launched and if you do you may suffer criminal penalties,” said William C. Banks, a law professor and Director of the Institute for National Security and Counterterrorism at Syracuse University.

The federal code has 21 statutes outlining the different methods of obstruction of justice, including the use of murder or physical force to disrupt a testimony influencing a juror, and falsifying records. But one of the statutes, 18 U.S. Code § 1512 also includes a general provision, explaining that someone who “otherwise obstructs, influences, or impedes any official proceeding, or attempts to do so, shall be fined under this title or imprisoned not more than 20 years, or both.”

But the key to proving obstruction of justice, explains Robert Weisberg, a law professor at Stanford, is that the intervention has to be propelled by corrupt motives.

“If it’s a threat, that makes it a crime. If it’s not a threat — but a request — it could still be a crime if the threat is motivated by a corrupt purpose,” Weisberg said.

The punishment varies, and usually depends on what the person was convicted for, but the maximum is 20 years of imprisonment if fined under the federal statute of 18 U.S. Code § 1512. In 1974, articles of impeachment drafted against Richard Nixon accused him of obstructing justice after he refused to hand over his tape recordings to the FBI. Nixon resigned, but faced no charges because Gerald Ford pardoned him.

In 2007, then Vice President Dick Cheney’s former Chief of Staff Scooter Libby, was convicted of obstruction of Justice — in addition to lying to a grand jury and FBI agents— regarding the federal investigation into the leak of the identity of Valerie Plame and received a 30 month prison sentence before President George W. Bush pardoned him that June.

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Write to Alana Abramson at Alana.Abramson@time.com.