Things just don't seem right with your beloved lawnmower: it's behaving a bit oddly and there's a strange sound emanating from the mower deck. You turn off the engine, and fall to your knees to investigate. After a few minutes of searching, you discover the source:
It's round, a v-belt runs through its grooved edges, and there's a hole in the center to attach it to the shaft of the motor... Your vast experience in this arena tells you it's a v-groove drive pulley. After removing the damaged product, you locate your lawnmower manual, and (with the use of a high-powered microscope) are able to decipher your Genuine OEM Part Number
The description next to the part number says "Sheave, 7x3/4"
You see black around the edges of your eyesight... Now you have to question everything! Is the world truly spinning, or is it just you? How have you gone your whole life calling this a drive pulley, if it's really a sheave?
Take a deep breath, you're not alone in this dilemma. This is, one could argue, the ULTIMATE QUESTION:
What is the difference between a pulley and a sheave?