Longman Dictionary of Contemporary English
WordNet
n. a stone laid at a ceremony to mark the founding of a new building
Wikipedia
The Foundation Stone ( Hebrew: אבן השתייה Even ha-Shtiyya or סלע Sela, Arabic: صخرة Sakhrah "Rock") is the name of the rock at the heart of the Dome of the Rock in Jerusalem. It is also known as the Pierced Stone because it has a small hole on the southeastern corner that enters a cavern beneath the rock, known as the Well of Souls. It is the holiest site in Judaism (Midrash Tanhuma, chapter 10); Jewish tradition views it as the spiritual junction of Heaven and Earth. Jews traditionally face it while praying, in the belief that it was the location of the Holy of Holies in the Temple.
Foundation Stone is the name of the rock situated under the Dome of the Rock in Jerusalem.