Freezer burn is a food-quality issue, not a food safety issue. It appears as grayish-brown leathery spots on frozen food. It occurs when air reaches the food's surface and dries out the product. This can happen when food is not securely wrapped in air-tight packaging. Color changes result from chemical changes in the food's pigment. Although undesirable, freezer burn does not make the food unsafe. It merely causes dry spots in foods. Cut away these areas either before or after cooking the food. When freezing food in plastic bags, push all the air out before sealing.
Source: Excerpted from FDA/CFSAN Food Safety A to Z Reference Guide, September 2001