A sacrifice fly is a fly ball that is caught for an Out, but that allows a runner to tag up and score. A sacrifice bunt is a ball that is "tapped" with the intent of sacrificing an Out (the batter) to advance the runner or runners on base.

Yes. While a sacrifice fly does not count against your batting average it does against your on base percentage.

On base % = (hits + walks + hits by pitch) / (at-bats + walks + hits by pitch + sacrifice flies)

A sacrifice bunt or fly has never been considered an at-bat.

A sacrifice fly in softball is when they batter sacrifices themselves (meaning they are getting an out) to score the runner or to move the runner into scoring position.

A fly ball that advances a runner from second to third is not counted as a sacrifice fly, and it does count as an at bat. Unless a runner scores on a fly ball, the batter is charged with an at bat.