NOD Theory was created by an individual during a lecture at University of Canberra. This individual was bored with the content of the lecture and decided to spend the rest of his time picking up chicks, this is how the Nod Theory was created.

The Nod Theory is when you make an eye connection with an attractive young female, look at them for several minutes indicating you attraction, while having a smooth and sexual smile on your face. You later make a second connection with the female and give her the "Nod" indicating, How you doing? Im into you, lets chat!

Noun: a friend who is usually only called upon by a friend when a more primary/prominent friend is unavailable.

Taken from the term “second string” in an athletic competition situation. In football, if the star quarterback gets injured during a play, the second string is called off the bench to replace him/her. A “Second String Friend” is essentially benched until needed, if ever.

Synonyms: Plan B, Second Choice, Secondary Friend, Benched Until Needed