Protocols

TCP - Transmission Control Protocol. The old and still most dominant way to package up data to send across the internet. This handles things like retransmitting data if some gets lost and is pretty robust and full featured, while having some overhead to provide those features. Speed tests that use TCP will automatically have a lower number because of the extra data.

UDP - User Datagram Protocol. A much simpler way to send data with fewer features and less overhead.

QUIC - Quick UDP Internet Connections. Rapidly replacing TCP for services providing better than UDP features but without the overhead of TCP.

ICMP - Internet Control Message Protocol. Can do a lot of things... but for most this is 'ping' or a latency testing (NOT measuring) tool.

'the rest' - there are hundreds of protocols in use, too many to define at the moment, and most of them aren't really anything a consumer will run across in a conversation unless it's with a professional nerd.