The checkout is the second stage of the eCommerce purchase flow: cart; checkout; order.
A checkout holds information about items to be purchased, price and tax summaries, shipping and billing info, any applied discounts, and more.
The eCommerce Checkout API currently provides functionality for retrieving checkouts and listening to events when a checkout is created, updated, and marked as completed.
To assist in migration from the Stores to eCommerce APIs, please refer to the Stores Cart to eCommerce Checkout Conversion Table.