The related source code from ST is generally also commented explaining some of the outline, use and context.
Double buffering in ST's naming relates to using Two distinct memory buffers (address, and size) for DMA data into/out-of, and alternating between the two.
Perhaps like a Ping-Pong concept that walks through memory as it would allow you to change the address of the inactive buffer, whilst the DMA unit deals with the active one.
