True love is supposedly affection of the 'written-in-the-stars', fate and destiny brand. It occurs only once in the lifetime of your average character, and is often the source of much joy, angst, moping, irrational moodswings, Famous Last Stands, Deus ex machinae and unexpected plot twists. Note that in real life, true love can occur more than once in a person's lifetime, and many good works of fiction may deal with this fact.
Unless you're a Suethor, in which case the page you're actually looking for is here.