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SD - Secure Digital (memory card you’d use for most things)

FTP - File Transfer Protocol (a way to upload files to a server)

RTSP - Real Time Streaming Protocol (a way to stream video)

NVR - Network Video Recorder (a device that records video)

Reolink doorbell cameras don’t need to be connected to the cloud. They can record to an SD card or upload to an FTP server. You can connect to them with RTSP and run your own NVR if you want too.