Kodak's less popular 400 ISO Emulsion. Great film with plenty of latitude, ideal for learning!
Here is what Kodak say about there other 400ISO film
KODAK PROFESSIONAL T-MAX 400 Film ⁄ 400TMY is a continuous-tone panchromatic black-and-white negative film especially useful for photographing dimly lighted subjects or fast action, for extending flash distance range, and for photographing subjects that require good depth of field and fast shutter speeds with maximum image quality for the film speed. It is also useful for scientific and biomedical work, especially when fluorescence photography is required. It has high speed (ISO 400/27° in most developers), very high sharpness, very fine grain, and very high resolving power; it allows a high degree of enlargement.