Embedded system
Unlike a microprocessor for a general-purpose computer, bigger and faster is not always better.  Many embedded processors are very small.  Sometimes this is to use less space or less power, sometimes it is to be cheaper.  General-purpose computers will use microprocessors that read 32-bit or 64-bit words and run at speeds measured in GHz, but embedded processors are usually 4 to 32 bits and run at speeds usually measured in tens of MHz (a hundred times slower). (But the programs are also smaller and do not check for things that are not used).