Difference between embedded systems and System-on-a-Chip (SoC)?
Embedded System usually contain multiple chips inlcuding main microcontroller and some basic front-end (ADCs Op-Amps, Comparators, Voltage Regulators). By embedded system You can describe a piece of hardware.

System on Chip is basically an Embedded System but fully integrated on one Chip. SoC can contain both digital and analog circuits and sometimes even allow for connection configuration between the system elements like in Cypress PSoC chips for example.