Definition for Disulfide bridge
From Biology Forums Dictionary
A disulfide bridge is formed when a sulfur atom from one Cysteine forms a single covalent bond with a sulfur atom from a second Cysteine in a different part of the protein. This bond is termed a Disulfide Bridge; these bridges help to stabilize proteins, especially those secreted from cells. The presence of a pair of Cysteines in a protein indicates the possibility (but not the requirement) of a disulfide bridge.
Unlike a hydrogen bond, a disulfide bridge was not shown in the first implementation of FoldIt. Manipulating Cysteine sidechains so that their ends point toward one another has sometimes been noticed to yield points, but as it turns out, the developers have confirmed that this effect is unrelated to the disulfide bridge.