RAM - Random Access Memory
This is used to refer to memory in a computer or MicroController than can be written to, and read from in a random manner. Early memories used to be sequential only- that is - you could only read them out in the order they were written - kind of like a tape. Most memory these days can be classified as RAM.
Most RAM is volatile - that is, it will retain what is written to it, until the power is switched off - some kinds of memory - like Flash Memory are non-volatile, and will retain there memory for a reasonable time after the power is switched off.
Some RAM statically stores the data - when a circuit (a bit) is flipped to one state, it remains so until it is flipped the other way, or power is lost - this is called static RAM. A great deal more modern RAM is dynamic RAM, which is considerably cheaper - and the stored bits will gradually decay- so they need special control circuitry to continuously refresh the Bits.