A kind of pedal for high quality bicycles to which special shoes clip themselves. Also called, ironically, clipless because of their lack of more typical toe or basket clips. Mine cause me to fall down alot.

Stands for "Shimano Pedaling Dynamics", after the company that came up with them, or "Stupid Pedal Device" after all the cyclists who use them.

Mostly on mountain bikes, but becoming more common on road bikes.

Not to be confused with the Look^tm Pedal.

SPD is also an abbreviation for Serial Presence Detect. SPD is a chip found in DRAM memory which tells the host computer what type and size the memory is, along with any other info (presumably CAS and RAS strobe timings etc.)

And not many people know that...

(as a matter of fact, I didn't until recently)