Traction is a measure of how far a character can slide on the ground, either by shielding an attack or by wavedashing. In Melee is generally considered best for characters to have a moderately low traction, so they can wavedash an optimal distance . Luigi is known in all 3 games to have an extremely low traction.
This is a ranking of each character's traction in Melee, from least to greatest.
2. Ice Climbers (Except on ice, where their traction is best)
7-9. Dr. Mario/Mario/Mr. Game & Watch (all equivalent)
15. Young Link
17. Donkey Kong
18-19. Pikachu/Sheik (equivalent)
20-21. Captain Falcon/Kirby (equivalent)
25-26. Peach/Zelda (equivalent)