Random-access memory is a form of computer memory that allows any of it data to be read or written in any order.
Most modern RAM is SRAM or DRAM, both of which are volatile: the stored memory is lost when power is removed. Non-volatile memory exists in the form of ROM, and non-volatile RAM is in active development but not widely implemented.
Computer memory holds working data that is in use by the system, this data can also be held in other parts of the primary memory. Data in secondary storage (on the “disk”) cannot be accessed directly by the CPU and must be read into primary storage first.