microcontroller - What is SOC in embedded System

I am new to Embedded domain and wanted to know what exactly is SOC(system on chip) means?

Is it like we different hardware component on CPU chip(like RAM on CPU chip) or on the same embedded board we have cpu chip manufactured by one company and rest of the component are manufactured some other company.

For example I have heard of TI soc's and Brodcom soc's both share the same cpu chip .