The word carat comes from the Carob Mediterranean tree whose seed was used for centuries as the standard of weighing precious gems. Each carob seed weighs approximately one-fifth of a gram. A carat is one-fifth of a gram.
Jewelry & Diamond Industry Dictionary of Terminology
Personal ornaments, such as necklaces, rings, or bracelets, that are typically made from or contain jewels and precious metal.
"jewellery" is the British spelling of the word. As an American company, Walt's Jewelers proudly uses the American spelling.
Sources for these definitions are GIA.edu, Google.com, Meriam-Webster.com, and Wikipedia.org.