Pop-out
A small conical crater in a concrete surface left when a particle of aggregate just below the surface expands and breaks the concrete above it away.
What does pop-out mean?
Pop-outs are caused by unsound aggregate particles such as porous chert or shale that absorb water and expand when frozen, or by reactive particles. The crater usually has the offending particle visible at its bottom. They are cosmetic in most flatwork but can be numerous enough to be objectionable, and they indicate aggregate soundness rather than any error by the placing crew.
In practice
Scattered dime-sized craters appearing on a driveway after the first hard winter are pop-outs, and they are an aggregate issue, not a finishing one.