system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do dogs lick people?

Does it represent a particular emotion on their part?
gpt
The licking action is a sign of submission. When a dog wants to let another dog know that he's no threat he will do things that young puppies do to make him seem less aggressive. Sometimes it's done in excitement as well, to welcome the pack leader home. This comes from asking their mother to vomit up what prey she ate while she was gone. 

The dogs that do this most often are ones that are bred for keeping their juvenile traits, or dogs that are purely pets. Most dogs that work for a living show their respect and adoration in more adult ways. 

The exception is the slow, lazy lick of your hand or foot while you're both relaxing. This seems to be a form of affection, although they don't seem to do it to each other very often.