The Canadian Shield, also called the Precambrian Shield or the Laurentian Plateau, is a vast horseshoe-shaped area covering eastern and central Canada, and a small part of the northern United States. One half of Canada's area is occupied by the Canadian Shield.

Due to the effect of the most recent ice age, the Canadian Shield has very thin soil with rocky outcroppings frequently showing. It is mainly undulating land with small hills and with numerous lakes. It is unsuitable for farming, but large parts in the south have forests and mining is also fairly common.

I'm extremely grateful to Jeremy Whitlock (cz725@freenet.carleton.ca) who supplied the following explanation:

The Canadian Shield is also called the Precambrian Shield since it represents the exposed bedrock of the Precambrian Era. It is more correctly called the North American Precambrian Shield, since all continents have a Precambrian Shield (the North American is the most exposed). Americans tend to call it the Precambrian Shield, while Canadians prefer Canadian Shield.