https://math.libretexts.org/Bookshelves/Combinatorics_and_Discrete_Mathematics/Elementary_Number_Theory_(Clark)/01%3A_Chapters/1.04%3A_The_Floor_and_Ceiling_of_a_Real_Number
Aug 17, 2021 · Here we define the floor, a.k.a., the greatest integer, and the ceiling, a.k.a., the least integer, functions. Kenneth Iverson introduced this notation and the term