The official terms carpet and rug, are used to define size globally. A carpet is usually an item with an area of 4.4m² or larger (bigger size), and a rug is usually an item with an area smaller than 4.4m² (smaller size).
This specific distinction is not always made, in most occasions that is. Many countries, including the United States, use the term rug to describe all items regardless of size.
There are a few exceptions though. For example: ‘Prayer Rugs’ are never referred to as carpets, and anything that contains a hunting design, is called a hunting carpet not a hunting rug.
FUN FACT: Anything sold in Britain or the British Commonwealth is always clearly identified either as a carpet or a rug.
*Generally anything larger than 6’x9′ is considered a carpet*