A word uttered my two English-speaking humans when they first encounter each other.
It is used for calibrating the speech-processing wetware to compensate for accent,
pitch, volume, nasal congestion etc. It roughly translates as Can
you hear me? Are you willing to talk to me? By extension, the first exchange of
messages in a protocol. The term by extension refers to the first messages exchanged in
a computer communication protocol to establish that the identity of the other end and
its ability to communicate in the expected protocol.