Well love is complex and difficult to explain but lust is straight forward. There are different kinds of love and different ways people express love so I'm not sure there's on clear cut definition of love. If you ask me everyone has their own special way they define love and the best I can do is give you my point of view on just what it is and how it differs from lust.
Well you see, love for me is an intense feeling g which we feel for something or in this case someone which we may or may not be able to explain why we do, true love is often unconditional and doesn't require a reason for you to actually feeling it for someone.
Lust on the other hand is purely physical, it's basically the sexual desire for a person and is often confused with love because the intensity to which we feel lust is often very similar to how we feel love. The key difference is that with love you'll probably feel a sexual desire for the person, but you'll feel other things too, but with lust, all you feel is the physical sexual desire and nothing more.
In my opinion alot of what we say is love at first site is often lust at first site. What we see before we get to know a person is their physical attribute and if you feel a deep attraction for the person then most likely it's lust and not love.
I hope this helps.