An eggshell is the outer covering of a hard-shelled egg and of some forms of eggs with soft outer coats. The generalized eggshell structure, which varies widely among species ...
http://en.wikipedia.org/wiki/Eggshell

eggshell ( ) n. The thin, brittle, exterior covering of the egg of a bird or reptile. A pale yellow to yellowish
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egg·shell (g sh l) n. 1. The thin, brittle, exterior covering of the egg of a bird or reptile. 2. A pale yellow to yellowish white. eggshell [??g???l]
http://www.thefreedictionary.com/eggshell

Much information has been learned about eggshell quality during the past fifty years. During this period of time, the genetics of the chicken, diets, house design and management ...
http://www.afn.org/~poultry/flkman4.htm

?noun. 1. the shell of a bird's egg, consisting of keratin fibers and calcite crystals. 2. a pale yellowish-white color. 3. rather bulky paper having a slightly rough finish.
http://dictionary.reference.com/browse/eggshell