The angstrom (also Å or ångström) is a unit of length used in analysis of proteins. An angstrom is one ten billionth of a metre (10−10 m), 100 picometers, or 0.1 nanometers. See the wikipedia article Ångström for more fun facts.
In Foldit, bands have a length attribute that's measured in angstroms.
Angstroms are useful with proteins because many distances are in the range of 1 to 10 angstroms. For example, the sulfur atoms at the tip of two cysteines are ideally 2.05 Å apart when they are in a disulfide bridge.