Aron kodesh, sometimes spelled aron qodesh, (ארון קודש in Hebrew) is generally a receptacle, or closet, which contains the Torah scrolls in a synagogue. In most cases, when possible, the aron kodesh is located on the wall of the synagogue closest to Jerusalem. Literally, aron qodesh means "sacred closet".
The name is a reference to the aron ha-qodesh, the Hebrew name for the Ark of the Covenant.
More information can be found in the more exhaustive Jewish Encyclopedia (http://www.jewishencyclopedia.com/) article for "Aron Kodesh (http://www.jewishencyclopedia.com/view.jsp?artid=1778&letter=A)"