Both frogs and toads belong to the Order Salientia. Within that order we find the following frog and toad families represented in North America north of Mexico:
What's the difference between a frog and a toad?
The easiest-to-see distinction is that toads have warty skin, while frog skin is relatively smooth. That's a Bullfrog at the right, so you can see that its skin isn't nearly as warty as the toad at the bottom of this page.
One way to decide whether a backyard frog belongs to the "True Frog Family" is by the process of elimination. The vast majority of backyard naturalists will very seldom or never see members of families listed above as "uncommonly encountered." Most of those families are found in restricted geographical areas, or else -- as in the case of spadefoot toads -- the toads may be present, but very secretive.
Therefore, if you learn to identify treefrogs and toads and decide that your critter is neither of those, then just about every other froggy creature you find will be a "true frog," a member of the Ranidae.
The frog at the right can be recognized as belonging to the Treefrog Family because of its small size (up to 2.5 inches long -- 7 cm). Also, its feet bear conspicuous rounded pads at the tips of its toes. Those pads are adhesive pads enabling them to, among other things, stick to the vertical aluminum siding of my trailer! This particular little beauty is the Barking Treefrog, Hyla gratiosa, of the southeastern US. Its mating call is a single, bell-like note, but sometimes it also gives loud, barking "rain-calls" from high in the trees. A few treefrogs, such as the cricket frogs (genus Acris) have toes without pads.
Above, you see a Pacific Treefrog, Hyla regilla, crouching on a leaf about six inches above the water of a small backyard pond. If you spot a treefrog, he'll probably be crouched just like this one -- so that his diagnostic toe pads will be hidden! One treefrog feature this particular frog can't hide is its small size. It is less than two inches long. Most "true frogs" are much larger, and probably they wouldn't be adhering to and crouching on a leaf surface like this.
The two most conspicuous features indicating that the individual at the left is a toad, and a member of the Toad Family, are:
Those "growths" are parotoid glands. They secrete a viscous, white poison which smears into the mouth of any animal unwise enough to try to eat a toad. Depending on the animal and its size, this poison can inflame the mouth and throat, cause nausea and irregular heartbeat, and sometimes even kill the animal!
There's more about toads on our Toad Page.