Is a lien release the same thing as a lien waiver?

No. Depending on where you are the definition of a lien waiver changes. In most places, a lien waiver is a “receipt” that states the debtor (person who owes a balance) has paid in full the debt and that payment was accepted waiving right to place a lien on the property.
A lien waiver is the document used before filing a lien.
A lien release (or lien cancellation) is the document that releases a lien that has already been filed.