friend
companion or acquaintance whom one regards with affection, affinity, or loyalty
fuck buddy
friend seen primarily for sexual relief
friend of a friend
human contact that exists because of a mutual friend
girlfriend
regular female companion in a platonic, romantic or sexual relationship
close friend
someone's close friend
imaginary friend
phenomenon where a friendship or other interpersonal relationship takes place in imagination
pen pal
one of at least two people who regularly write to each other, particularly via postal mail