It depends on if you're keeping score or not.

If you make an attempt to hit the ball, you count a stroke. Whether the ball moves 1/32" or 300 yards, if you swung with the intent to hit the ball, it's a stroke. (Which is part of the reason why high handicappers are high handicappers).

If you're not keeping score, then it's a practice swing really close to the ball.

A guy I play with had to learn to back up to take practice swings the hard way - he used to stand close to his ball to take his swing - until one round where he clipped his ball on six different occasions - adding six strokes to his score.

The USGA rules this way:
18-2(a). By Player, Partner, Caddie or Equipment

When a player’s ball is in play, if:
the player, his partner or either of their caddies lifts or moves it, touches it purposely (except with a club in the act of addressing it) or causes it to move except as permitted by a Rule, or
equipment of the player or his partner causes the ball to move,
the player shall incur a penalty stroke. The ball shall be replaced unless the movement of the ball occurs after the player has begun his swing and he does not discontinue his swing.

Decision 18-2a/20 Ball in Play Moved Accidentally by Practice Swing
Q. A player makes a practice swing and accidentally moves his ball in play with his club. Has he made a stroke?

A. No. He had no intention of moving the ball — see Definition of "Stroke."
However, he incurs a penalty stroke under Rule 18-2a for moving his ball in play, and the ball must be replaced.

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True Length Technology Fitter - www.truelengthtechnology.com
It's live! - www.ShipShapeClubs.com
PCS Class 'A' Clubfitter

A new highlight: Golfing the home course on Christmas Day.

I say it too often: If it's golf club shaped, you can play with it.

For the record, I'm a club doctor, not a swing doctor.