What does BCD mean in reference to bikes?

Bolt circle diameter. It is the spacing of the bolts that hold the chainring on the crank.

See here for all cycling terminology: https://sheldonbrown.com/glossary.html

Bouyancy Compensation Device

Oh, bikes... Never mind!

+1

You shouldn't joke with people who aren't sure it's a joke.

Hence why i said related to bikes.

Open Water 1 certified. don't have enough nearby to go for OW2.

I'm a NAUI, not one of those PADI folks... pretty awful diving instruction.

One way to think of it is imagine a perfect circle that passes thru the center of each bolt, the diameter of that imaginary circle is the BCD.

Sheldon's site offers a practical way to measure BCD, instead of drawing and measuring a circle.

All right, now that the question's been answered... time for some alternate definitions:

Butt Crack Dirt

Cause: Riding in the rain with no fenders.

I kinda figured when you made that distinction so clearly.

My last re-cert was through NAUI; I share your opinion of PADI. I've been certified in one form or another since the late 60s when they taught out of the US Navy Diving Manual because that's about all there was. Learned the internals of one and two-stage regulators as part of the basic cert. We called BCDs "BC"s for Bouyancy Compensator, and take if from a guy that dove for years without one, they're a mixed blessing. Nice not to have to be so precise with the weights and not have to swim to maintain depth, but they also add a good bit of complexity and aren't cheap. The comfort of the integrated backpack is probably enough to swing the balance toward using one - I do. (That and not freaking out your instructor.)

Where abouts are you?