Sequential Access Memory is a type of memory
wherein the data
contained in the memory can only be accessed sequentially--that is, if the last address to be read was 'M' and you wish to read the data at address 'M+7', you must read all of the data in between, you cannot go directly to 'M+7'.
For example, consider a tape drive: in order to fetch some data, you must scan over all of the data between the current address and the desired address. This is because the tape must be physically moved either forward or backward to position the right portion of tape under the head.
Oppose: Random Access Memory.