Amaranth's Guide to Filter Masks Part 1

I am by no means a professional. I did some research on DoA (there are really great threads with good information there), as well as on the internet. Knowing that many people don't have access to DoA, I thought I'd do a simple hobbyist's guide to filter masks. I tried to keep it really simple and not wordy.

Here is part 1, just some basic Q & A and terms. I'll go into detail about numbers and what they mean in the next post.