Here is my answer:
Processor can be categorized into 3 type (based on a book I have read): microprocessor, microcontroller, DSP processor.
Microprocessor is a general purpose processor use for general applications.
Microcontroller is a lower performance processor use for embedded systems for specific target applications such as display controller in the mobile phone.
SoC is a short for system on chip. It is a technology where we integrate different architectures/blocks in a silicon die to form a complete system. Example, Apple A4 SoC which has GPU, ARM CPU core, DDR controller. You can find the die photos from google.
Hope it helps.
Thanks.