You haven't indicated how old this tree is or what time of year this happened, so here are some general suggestions or things to look for. You may need to seek the advice of a qualified arborist if you cannot determine exactly what the problem is.

Trees may suffer from a fungal disease called Hypoxylon canker. Peeling bark, wilting leaves and a mat of fungus may be some clues that this is the problem.

Temperature stress also can make bark pop off. If you've experienced sudden swings in temperature, such as excessive heat or frost damage, this could be the culprit. 

Insect infections, which might include insects burrowing in the trunk, could cause bark to fall off. 

Animals eating bark is quite common. Check other trees in your area to see if bark is missing at about the same level, which could indicate deer or other animals removing the bark.

Finally, trees do simply shed their skin (the bark) like a snake because the trunk needs to enlarge. This isn't a problem unless open wounds occur, which could become infected. The bark will not grow back or cover a large "naked" area.

Again, watch for other signs and symptoms of problems, and consult an arborist if you want additional information or details about treatment for a pest.