What does it mean when a WNBA player is waived?

When a player is waived, it means that the player's team has given up their right to retain that player.

Her team still has to pay her contract until another team either claims that contract (in which case the claiming team assumes the contract) or negotiates a new contract after the player has "cleared waivers"

To clear waivers means that no other team has submitted a claim to that player's contract. Different professional sports leagues have different waiver rules.