On the small, contextual instructions that often appear inside or next to web forms:

Ironically, the smallest bits of copy, microcopy, can have the biggest impact.

Microcopy is small yet powerful copy. It’s fast, light, and deadly. It’s a short sentence, a phrase, a few words. A single word. It’s the small copy that has the biggest impact. Don’t judge it on its size…judge it on its effectiveness.

via Writing Microcopy « Bokardo – Social Design by Joshua Porter.