A family of Kodak black and white films used for, black and white photography, of course.
It was something of a revolution at the time, using modern chemistry so that the silver grains that make up the image on the film are small and tight. This leads to smaller grain on the film for a given film speed, relative to traditional films.
Of course, some people preferred the grain, so they stuck with something like Tri-X.
T-max films come in 100, 400, and 3200 ASA.
I believe some of the technology also went over to the way color film is made.
Ilford makes something similar, but they call it Delta.