A glacier is a big flow of ice, the growth of which is associated with the Ice Ages. The glacier fringe is the area where the glacier has recently melted.
Glaciers are basically patches of snow that do not melt in the Summer. Some are quite small. Others may be tens of kilometers in length. Today, they are found on very high mountains in equatorial and mid latitude regions and progressivly lower as one approaches the poles. Greenland and Antarctica are heavily glaciated -- to the point of being almost entirely covered by ice. Glaciers are really rivers of ice that move slowly downhill. Even in very cold climates, there may be unglaciated areas that receive too little precipitation to form permanent ice.
A number of geologic features are associated with glaciers including moraines that form from glacially transported rocks at the terminus of the glacier; distinctive U shaped valleys; cirque valleys at their heads; distinctive hills known as drumlins; and streambeds under glaciers known as eskers.
During ice ages continental glaciers may be as much as 1500 meters thick.
In the past several centuries, glaciers have generally been retreating -- often dramatically.