With RAM the data is being stored as a voltage level continuously refreshed by computer. When the power is removed, the refresh voltage disappears, and the data it represents disappears. This is volatile storage. Infinite re-writes of the same bits, but data cannot persist without power always on it.

With NVRAM aka Non-volatile RAM (which is what SSDs are) data is being stored in a physical material. When data is written, the data represented by voltage differences, is used to make a physical change via chemistry to the material that makes up the SSD. This is also a MUCH slower process in NVRAM than updating data in real RAM. However the benefit is, because NVRAM is a physical change, you can remove power, and the data persists. When you power it back up, the data is read from the physical shape of the chemical material that makes up the NVRAM and then represented again as voltage differences when passed back to the computer.

The cost to this is there are only so many times that the chemical material can be changed. It wears out and is eventually no longer changeable.