I am a single-pass compiler.
Why?
Well, when I have to do the food shopping for the week, I have a look at the buying list, keep the things in mind, go through the shop exactly once and everytime I see a match with the list, I put it into the shopping trolley.
Efficient and quick.
Soo, on the other hand, my girlfriend is a multi-pass compiler.
What that mean, you ask?
Well, she doesn't have any look at the buying list until she is in the shop. Then, she runs through the whole building until she finally finds the first thing on the list... and repeats with the next one until there's no entry left.
She needs three times longer than me for this, is totally exhausted after it, and, not forgetting, then SHE is angry about ME, because I wanted to have these "special" sweets she had too run through the shop twice for because she couldn't find it at first try.