When is implementation of a Product Backlog item considered complete?

According to the Scrum Guide1, an Increment is a concrete stepping stone toward the Product Goal. Each Increment is additive to all prior Increments and thoroughly verified, ensuring that all Increments work together. In order to provide value, an Increment must be usable. Multiple Increments may be created within a Sprint. The sum of the Increments is presented at the Sprint Review thus supporting empiricism. However, an Increment may be delivered to stakeholders prior to the end of the Sprint. The Sprint Review should never be considered a gate to releasing value. Therefore, implementation of a Product Backlog item is considered complete when the item has no work remaining in order to be potentially released.