1) (Making out to someone) To flirt excessively and/or inappropriately.
2) To kiss someone repeatedly and/or for an extented period of time, sometimes accompanied by "touching".
I saw her at the partylast night... she was making out to Joe like you wouldn't believe. He must have noticed, 'cuz a while later I saw them making out in the backyard.
In my teenage period (1950s) making out was 'going all the way.' Sometime since, making out has come to mean petting (groping, touching, fondling). The word petting seems to be vanishing in the 21st Century.
Before grandfather and grandmother married, they had sexual intercourse (fucked) in their teens but that sounded so harsh, so they called it making out.