It may seem like a silly answer, but jumbo frets are just taller and wider than normal frets.
I guess you really need some point of reference to know what I am talking about. Most modern Ibanez guitars come with jumbo frets, and you would find normal frets on the vintage Strats, among many others.
Jumbo frets somewhat mimic the effect of scalloping your neck, of course to a much less drastic extent.
They afford you more room between your strings and the fingerboard, and this allows you to grip and dig in to the strings better, making bending and other techniques easier.
And for one I would assume they last a lot longer as well as compared to normal frets. I read somewhere that Buddy Guy changed his frets to jumbo ones because the normal ones were just wearing out too fast with his constant gigging.
But I always have a problem with sliding on jumbo frets. So at the end of the day, it is all down to personal taste and playing preference. Some guys swear by jumbo frets while others by medium/vintage thin frets.
I say go give them an extensive try-out and see what you like.