Rockwell is a very popular slab serif, or Egyptian, typeface. In this style, which is getting super popular now, the serifs are usually unbracketed and have the same stroke weight as the main strokes (i.e. they’re really big). They also tend to be a bit like some Grotesque sans serifs, like Akzidenz-Grotesk.
Rockwell is more of a Geometric style, meaning it’s made of simple shapes—similar to Futura—with a few notable exceptions (the lowercase a, for example, doesn’t fit the normal single-story Geometric template).
Rockwell was designed in 1933 and is a popular choice for display type (titles and large text). Because of its fat serifs and heavy weight, it’s not suited to body text.