Rainbow board
Basic Definition
A rainbow board in poker refers to a situation where the three cards on the flop are all of different suits. In this scenario, a flush draw is not possible, which limits the potential for certain draws.
Specific Situation
If the flop is 

, all three cards are of different suits, making it a rainbow board.
Similarly, when the flop is 

, the cards are of all different suits, so there is no flush draw.
Important Information
On a rainbow board, since there is no possibility of a flush draw, players' actions tend to be based on straight draws, existing pairs, sets, top pairs, and so on.
Since there's no need to worry about a flush draw, there are more opportunities to play aggressively. However, you need to be cautious of other strong hands, such as sets or straights.
Examples of Term Usage
"This flop is a complete rainbow board, so there's zero chance the opponent has a flush draw."