Memory Interface -- There are several memory interfaces throughout a computer system. As it pertains to the GPU, a Memory Interface is the physical bit-width of the memory bus. Every clock cycle (billions per second), data is transferred along a memory bus to and from the on-card memory. The width of this interface, normally defined as "384-bit" or similar, is the physical count of bits that can fit down the bus per clock cycle. A device with a 384-bit memory interface would be able to transfer 384 bits of data per clock cycle (there are 8 bits in a Byte). The memory interface is also a critical component of the memory bandwidth calculation in determining maximum memory throughput on a GPU.
Let's establish an imaginary GPU with a 1000MHz memory clock. At 1000MHz, or 1,000,000,000 Hz, the GPU will execute 1 billion clock cycles per second, each capable of processing instructions. A 384-bit memory interface on our imaginary 1000MHz memory clock GPU would be able to transfer a maximum of 384 bits of data on the memory bus one billion times per second.