In the Bible the Ark of the Covenant is a gold-covered wooden chest that Israel is commanded to build in Exodus 25, meant to hold the stone tablets of the law and to stand in the innermost part of the tabernacle.
Exodus 25:10-11 in the King James Version reads:
10 And they shall make an ark of shittim wood: two cubits and a half shall be the length thereof, and a cubit and a half the breadth thereof, and a cubit and a half the height thereof. 11 And thou shalt overlay it with pure gold, within and without shalt thou overlay it, and shalt make upon it a crown of gold round about.
These verses appear in Exodus 25, in the instructions God gives Moses for building the tabernacle and its furnishings. Read it in context at Exodus 25:10-11, or the full chapter at Exodus 25. Encyclopedia entry: en.wikipedia.org/wiki/Ark_of_the_Covenant.