“This was not lichatchila part of the Beis Medrash; it's a hasafa.” (Weiser)

“The harmony was my hasafa to the nigun.” (Weiser)

“My paper came back with so many hosafos, I'm surprised I got a grade for it.” (Weiser)

"This Shabbat (Vayakhel/Pekudei), the gabbai called up a levi for shvii, and as ba’al korei, I knew he was going to make a hosafa and give acharon/chazak to someone else." (source)