Random Access Memory (RAM) takes its name from the fact that any part of the memory can be addressed instantly; there is no need to read through the memory sequentially, but many other types of memory are also random access without having all the caracteristics of RAM. For example, most types of ROM are, in face, able to access data randomly.
RAM is typically very fast, does not retain the values stored in it after power is removed, and costs more per byte than any other type of memory.
It is used when speed and rapid (random) access is critical; for example, in the processing of programs and data by the CPU of a personal computer.
RAM can be made from flip-flops (Static RAM) or from a charge coupled device (Dynamic RAM).