First Base
In relationship/sexual terminology, this is the Stage in dating where the couple kisses, or makes out.
It is the First Stage, starting with the first kiss, and leads to repetition to say Goodbye or Goodnight.
It signify's the Beginning of being in love.

This can lead to French Kissing, or kissing of the Tongue.

This is the Beginning of Courtship, or a Physical-Loving Relationship that naturally resolves to advancing sexual stages until 'Home Plate'.
"Jimmy made it to First Base with Kelly today!"
"Congrats to him - Maybe he can find that Gum I left in her mouth last week..."