Bob213 is correct. The true deep cycle has thicker plates which store electricity to be used for longer term power draws for lights,water pumps and circuits boards in RV's. They are heavier and more expensive.
Hybrids, which also work very well in RV use, have a thinner plate which also stores power but allows quick powerful bursts of electricity for starting or cranking an engine. This is called cold cranking amps..CCA = a rating on hybrid deep cycle batteries as well as car batteries. True deep cycles normally do not have CCA ratings.
Hybrids became popular for marine use to start the boat as well run all the electronics for navigation and fishing. They can discharged and charged many more times than a standard ( thinner plated ) car battery, making a good general choice for the RV'r.
http://sciencing.com/marine-vs-deep-cycle-battery-5606295.html