Explain to me “pending transactions”

[NoMoreE46]

Please explain the reason/logic for “pending transactions.”

Is the 'pending' part from the vendor-  let's say Home Depot?

Does HomeDepot hold all of its card payment transactions and  then transmits/requests on only certain days of the week?

Or is the pending due to the amount being released by the credit card company  (say Capital One) to HomeDepot's bank?

I know this may get more technical but thought I get some insight here.

[blindambition]

Pending transactions are either preauthorized transactions which confirm funds are on card. They are Also actual transactions not completed. Transactions usually complete to posted within a few days. Slow posts happen by vendor, as well as card issuer.