A pre-authorization (also “pre-auth” or “authorization hold”) is a temporary hold on your credit card in the amount of your purchase that typically lasts around 30 days, or until the post-authorization (or “Capture”) comes through.
This hold may show up in your account as a "pending charge". Pending charges immediately reduce your available spending balance by the amount of the purchase however there is no interest applied and until the transaction is finally captured no payment is due on the amount.
If there is a change to the purchase amount (for example something is out of stock and you cancel the item or change the quantity) the final amount posted will be less than the pre-authorization amount. Once captured any funds that were held in excess of the final capture amount will no longer be held.
We do a pre-authorization at the time your order is placed and a capture (charge) when it is shipped.
If the charge was declined you may still see a temporary hold on the funds as the bank shows that the card had an attempted charge.