The abbreviation "8GB DDR2" refers to 8 gigabytes of RAM. "DDR2" stands for double data rate, which allows the memory to move data at twice the speed relative to synchronous dynamic random-access memory, an older type of memory.
In 2000, DDR memory replaced its predecessor, SDRAM, because it allowed for a more effective transfer rate. In 2003, DDR memory was replaced by DDR2 memory, which cut the internal clock rates by half, allowing it run more efficiently. In turn, it was replaced by DDR3 memory, which made its debut around 2007. DDR2 memory is no longer considered to be standard.