Gateways such as Authorize.net and NMI sit between your checkout and your merchant account. Keeping the gateway separate from your store platform means a store change does not break your card payments.
Payment gateway
The service that takes card details at checkout and passes them to the bank.
See it running on your own catalog
Purity does the work these terms describe: batches held until their lab report is in, payments matched to orders, and wording checked before it sends.