Action cards are any card that is not a number card. There are 4 types of action cards...
1. Wild cards (either regular or +4 wild, these change the color to any color of your choice)
2. skip cards (these skip the next players turn when played)
3. draw 2 cards (these force the next player to draw 2 cards)
4. reverse cards (these reverse the order from left to right, or right to left)
Any combination of 100 of these cards over multiple matches will net you this achievement.