What does it mean when a woman makes a “it’s small” with her hand?

[LinkxPeach]

We had cake as a celebrity of the pastor’s graduation at church. Early today, I went to talk to my female friend. She went to get a slice of cake, but told someone, “she’s going to get a small piece.” She put her index finger, and thumb together to make something look small.

[Sour-rose]

The dude's weiner is small as my fingernail is what it usually means.