It’s a distinction no family wants.

“I am a Gold Star mother,” Ghazala Khan wrote in an op-ed article in The Washington Post on Sunday in a rebuke to Donald J. Trump, who had criticized her for standing silently by the side of her husband, Khizr, as he gave a memorable speech at the Democratic National Convention in Philadelphia last week.

Ms. Khan was invoking a term that signifies the mother of a fallen American soldier. Her son, Capt. Humayun Khan, was killed in Iraq in 2004, and she suggested that she had kept silent to control her grief at seeing his picture displayed behind her.

Mr. Trump’s attack on the parents of a fallen Muslim-American soldier has been denounced by veterans groups and has drawn bipartisan criticism, including a remarkable reprimand by Senator John McCain. But what does the phrase “Gold Star mother” mean? Here’s a primer.

Where did the term come from?

It dates to World War I, according to the United States Army. Families with relatives in the armed forces flew flags and banners with a blue star for those serving in wartime or during other hostilities. The flags are authorized by the Defense Department. If the service member is killed, the blue star is replaced by a gold one.