Leather is "animal skin dressed for use," according to the Merriam-Webster dictionary. Cowhide is a type of leather, but just one form of it. It is also the most plentiful and most common.
Leather is the tanned flesh of any animal. The most common after cowhide include deerskin, goatskin, kid and calfskin, pigskin and buffalo.
A practice unique to cowhide vs. other leather is splitting. The thick cowhide is separated into two or more layers, called "splits." The outermost, highest-quality layer is known as "top grain," while the splits are less durable and expensive.
Because cowhide is a byproduct of the beef industry, it is the most readily available and least expensive of leathers. Tandy Leather Factory sells a top-grain cowhide for as low as $4.99 per square foot, vs about $8 for rawhide goatskin as of February 2010.
Unless otherwise specified (as eelskin, kid skin, calfskin), any leather object you purchase, including shoes, wallets, furniture and auto upholstery, is fabricated from cowhide.
Cowhide is easily stamped and colored to imitate other leathers, including ostrich, alligator and elephant hide.