WASHINGTON — Donald J. Trump said during the campaign that he had a secret plan for the fight against the Islamic State. Eight days into his presidency, he seems to have revealed a small part of it.

ISIL is out. ISIS is in.

An executive memorandum that Mr. Trump signed on Saturday afternoon in the Oval Office repeatedly referred to the Islamic State as ISIS — not ISIL, as President Barack Obama and the rest of the federal government had called the terrorist group since 2014.

“This is the plan to defeat the Islamic State of Iraq and Syria, in other words, ISIS,” Mr. Trump said as he signed the memorandum, which called on the Pentagon to devise a “comprehensive plan” within 30 days.

The White House also used the name ISIS in summaries of the calls Mr. Trump had on Saturday with the Russian and French presidents.