RAM or Random Access Memory
RAM is the memory that information required by currently running programs is kept in, including the program itself. "Random Access" refers to the fact that it can be either read from or written to by any program. Many operating systems protect critical, occupied or reserved RAM locations from tampering.
ROM or Read-Only Memory
Memory that is stored on the hard drive of the computer. So-called because its contents cannot be accessed or modified by the computer user, but can only be read.
A router is a computer that sits between networks to direct packets to their final destination. Routers take the information held in packets and pass the packet along to the next available router that is closer to the final destination. Thus, depending on the amount of traffic that is currently on the network, different packets from the same message may travel different routes to their final destination.