The term "Oriental" generally refers specifically to rugs that originated in towns and cities in the contiguous land mass associated with the Safavid, Moghul and Ottoman Empires (modern Turkey, Iran, Afghanistan, India, and the Caucasus region). Rugs from China and Tibet also fall under the Oriental umbrella.
With a weaving tradition dating back to the 16th century, most rugs available today were woven between 1875 and 1930; old enough to have been created prior to the over-commercialization of the industry that resulted after World War I, but young enough to demonstrate the resilience needed to stand up to the demands of modern living.
As to what characterizes an antique rug, important is the fact that these pieces can be traced to the specific cities and regions referenced above, exhibiting distinct design and hues representative of these geographic regions. The materials used to construct the rug (wool, cotton, silk and animal hair), hues, motifs, type of knot and knot density coalesce to form a signature that validates provenance.
Within these general geographic categories there exists infinite variety, making each antique rug unique. Such individuality, combined with rich hues of wool and sophisticated designs, is what ultimately affords value to these pieces. As a unique work of art, the market value of an older rug can be verified based on its distinct heritage, condition, age and the harmonic execution of its design.