A common greeting used through text messaging, usually indicating the person sending it has a high level of interest in you. The higher amount of letter y's in the "hey", the higher the thirst this person most likely has for you. If over three y's, the sender has a complete and extreme level of interest in you, and can be considered a giveaway that they would like to bang you over a piece of furniture in the near future.
“Heyyyy” is another form of greeting, usually used by people in a relationship or sometimes as a simple joke. It’s also characterized as a meme where saying heyyyy means you want to have sex with the person you greeted it with.