It truely does depend on the venue that the speech is being given in. The situation matters quite a bit. Though you can really never go wrong with:
"Good morning"
"Good afternoon"
or "Good Evening"
The appropriate greeting for an email to a professor is "Dear Professor Last Name,"
The appropriate greeting to use when requesting a letter of recommendation is "Dear Recipient's Name."
Head nod
The appropriate way to respond to the greeting "Assalamualaikum" is by saying "Waalaikumassalam," which means "and peace be upon you too" in Arabic.
The greeting "good afternoon" is appropriate to use from around 12:00 PM until 6:00 PM.
It is a common noun.
The common handshake is enough.
The starting word of a speech is the introduction. Many people begin their speech with a greeting to the audience and distinguished guests.
The word hey is an interjection. It is an informal greeting.
a hard slap on the thigh
hi how are you? happy Good Friday
the appropriate thing is a comma