Some one everyone has, but the one no one on this earth has been able to meet. Your one true love is the person that is perfect for and you for them. They are everything you want and need. You love everything about them. And they return these fellings. If anyone could meet their one true love, well...that person's entire life would be complete hapiness. The two of you will never fall out of love.
A lot of people don't believe in a one true love, well those people obviously don't know of theirs.