In English, the pope said he is renouncing his role at the end of the month "because of advanced age." In some other languages, he uses the word "vacating."
This is a rare situation; the last pope to resign was Gregory XII in 1415.
But it turns out there is some specific language to help guide the linguistics of it all.
"Should it happen that the Roman Pontiff resigns from his office, it is required for validity that the resignation be freely made and properly manifested, but it is not necessary that it be accepted by anyone," according to laws that guide the church.
So according to those rules, the correct word to describe the pope's actions would be resignation.
But many people have been calling the pope’s announcement an abdication. That word normally applies in a royal context, when the person who leaves their position has an immediate successor in place.
In this case, the cardinals will vote on a new pope.