A toad is an amphibian of the order Anura, a classification which also includes the frog. I always thought the difference between toads and frogs revolved around the presence or absence of warts, but infoplease.com waffles a bit on this one. First it says that there's no clear cut distinction between the two. It says that colloquially, the name toad is used to refer to species with shorter legs, stouter bodies, and thick skins (no warts mentioned), while frogs are longer-legged and have more slender bodies. (Sounds like frogs are the supermodels of the Anura order.)
Then they go on to say that there is a family, Bufonidae, which are true toads. (Here come the warts.) True toads have bumpy skins and bulging glands behind their eyes. Unlike frogs, they are more terrestrial than aquatic and have feet that are "only slightly" webbed. I'm finding this all rather hard to grasp; it's just too subtle for me. So I'm just going to pretend toads are the warty guys, and continue on from there.
So these "true" toads, the ones in the genus Bufo, live near water in cool dank locales and absorb moisture through their warty skins. They give off a poisonous white fluid from their skins which stings if you touch them, though, contrary to popular belief, won't cause warts. Toads eat creepy crawly grub-like things. The females lay their eggs in strands of jelly in the water and males come and fertilize them. Like frogs, toads go through several stages of development, the tadpole gradually metamorphizing into the adult toad.
Some people keep toads as pets, especially the alarmingly-named fire bellied toad, which is however very tiny and not really scary at all. It can't stick its tongue out like other frogs and toads, and has to jump up to catch its prey. Find out about all about care and feeding of these beasties here.
Perhaps it's not surprising, given the warts and oozing poison and insect-eating, that toad is also a derogatory term for a really creepy or disgusting person.
For more toad-related information, see:
American toad
A toad can die of light!
cane toad
Colorado river toad
Frog and toad
Horned toad
I have a buddy. My buddy's a toad
licking toads
Mr. Toad's wild Ride
No toad sexing
noxious toad
sea toad
She axed me, so I jus' toad 'er.
Surinam toad
The Adventures of Ichabod and Mr. Toad
Them Toad Suckers
The Old Toad
Toadeater
toad in the hole
toad sexing
toad tunnel
toad the wet sprocket
toady
warty bliggins, the toad