Attack is an arcade game mechanic.
A dinosaur has three Attack stats, one for each Sign. Two of them are usually the same, and the third is the highest, corresponding to that dinosaur's "critical move", which is the sign displayed on the card. Sometimes the three numbers are close together, while other times the critical move is far stronger than the others. Upon winning a Rock-Paper-Scissors move button match-up with the opponent, a dinosaur will inflict the Attack of the Sign they won with as damage to deplete the opponent's health bar.
Only certain releases of the arcade cards show the three Attack stats, which can lead people less familiar with Dinosaur King to incorrectly assume that the dinosaur's Power/Strength stat relates to their attack (it's actually their health).