Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
I'm no expert in communications or digital buffers, but I think that in this case "Q" is short for "queue" (pronounced "cue"), which has various meanings. In electronics, it means a buffer like a FIFO (first-in, first-out memory). If more data comes in than the buffer can handle, it overflows.
Look up the definition of "queue" on Google.