A cart is an in progress Order that has not yet been completed, and can be created through Staff View or Community Hub. Carts save themselves as you proceed through the order process, and are converted to an Order once they have been submitted, with or without a payment.
If you make a payment in Staff View on a cart and save a credit card payment, but do not submit the cart, the payment will still be sent to your Payment Gateway as the save button during this portion of the order process is directly linked to the gateway to authorize the card in question. This will show as a Cart Payment and Cart Payment Line in the respective related lists on the cart.
There are a few fields on the cart that help communicate it's purpose:
Entitycontains the entity of the Community Hub constituent's are using.