Whole volumes have been written about this. Whole forests have been cut down to supply the paper to write about it. I'll give you my insignificant opinion. It is a condition where another person's happiness is essential to your own.

Just when another person means the whole world for you.

The true love is an inimitable feeling when your soul sings, the heart smiles and eyes shone with happiness..!

Can't say it better than fdmaxey. You can read books about it. Not a very good question to ask here :P

True love, what a delicate and cliche subject. What is true love? Who knows! Most people would throw around quotations or their own interpretation of what they have seen in movies, but who really knows what true love is like? It's true what fdmaxey said, and what every other person who have answered this question have nicely stated, but I believe true love is too much of a vast and complex subject to be able to be explained. What is true love? No one will truly know until they experience it. Yet, despite this, I'll try to explain: true love is like riding a couples bike. You depend on each other to go forth. It's not love that never sees darkness, or love that stays together no matter what and are always happy. No. True love is difficult, it's painful but most of all true love is hope. Hope in yourself, hope in another person. When one falls, or loses balance, the other one does as well and both fall together, then both get back up together, lending a hand to the other. I cannot elaborate for I am pressed for time but if you really want to leaen about true love, I hope you're one of the lucky ones who get to feel it. Many claim to know it but few actually know what it's like.