Window Dressing
Window dressing is the act of purposely flashing a card from your closed hand, so that others can see it. A player does it to give a false impression of his hand.
The simple explanation
If a player lets one card show, he may want others to see it. For example, he may show a card of a flush draw to make others believe he has more than he has.
A closer look
Window dressing is a form of acting. The visible card may be real or a part of a bluff, and it is risky because it can also give away information that is useful to the opponent. Some rooms treat exposed cards in different ways, so a deliberate flash may be penalized. It is not a recommended tactic, and most skilled players think that it is not worth the risk.
A practical example
A player slides one card up slightly to show a king and bets, hoping others believe he has a pair of kings.
Full explanation
Window dressing is the act of purposely flashing a card from your closed hand, so that others can see it. A player does it to give a false impression of his hand.
Window dressing is purposely showing a card from your closed hand.
The aim is to mislead others.
It can give away information.
Rooms may penalize it.