The rim of a coin

Coin

A coin is a piece of hard material that is standardized in weight, is produced in large quantities in order to facilitate trade, and primarily can be used as a legal tender token for commerce in the designated country, region, or territory....

 is the sharp circular (or otherwise shaped) edge which surrounds the coin design.

This is the part which exceeds the area of the die which strikes the coin during production, and as a result is pushed upward and sharpened to form a sort of border around the coin's design. The raised rim reduces wear on the face of the coin.

For accessibility purposes, the rim of the coin is sometimes milled with certain patterns in order for the blind

Blindness

Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...

 to more easily distinguish between coins. In Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, the two dollar coin has periodically distributed around its edge a short set of grooves, which alternate between the smooth rim, whilst the one dollar coin has a larger set of grooves, and the similar sized ten cent coin has grooves continuously about its edge.