Lens EF (Electrofocus) = This type of lens is intended for the type of Full Frame camera sensor that has a large lens diameter. This lens is marked by a red dot on the back. EF lenses are usually suitable for beginner DSLR cameras like the 1100D, 600D to professional 60D and 7D.
EF-S (Electrofocus - Short Back) lens = this lens type is specially designed for non-full frame cameras because of the smaller sensor size. This lens is marked with a white dot on the back. EF-S can not be used on Canon EOS 1Ds and 5D cameras.Thanks you @eosgo for the information. good information for photography