Rendering is the series of operations that determine the final pixel colour displayed for a frame of animation, and while this can be thought of broadly as rasterization, the actual conversion of the 3D scene into screen-addressed pixels, or "real" rasterization, happens during triangle setup, also called scan-line conversion.
In the case of graphics cards (or printers), this process turns an image into points of colour. A rasterizer can be a 3D card, or it can be a printer for that matter