Gold karat is an indicator of how much of the precious metal (gold) is contained in a piece made with it.
If a jewelry item is 18 karats, this means that out of a total of 24 parts, 18 parts of the piece are gold, and 6 parts come from other metals.
Expressed in percentage terms, 18 karats is equal to 75% gold content with the other 25% consisting of other, stronger metals.
The additional metals in 18K gold serve to make the blend harder and more durable than pure gold (24K), which is too soft for jewelry.
Pieces with 14k deteriorate at a faster rate than 18k gold jewelry, with shine and color fading over time.