Sleep tag excerpt:
A power-saving state, basically same thing as "Standby mode", that allows a computer to quickly resume full-power operation (typically within several seconds) when you want to start working again.
Suspend tag excerpt:
Questions related to Suspend Mode, which is a special low-power mode often used on laptops that preserves the contents of RAM while using less power than normal.
BTW, both tags need some review as they are question that don't fit within the description in the excerpt.