Definition: A thiol group is a fuctional group containing a sulfur atom bonded to a hydrogen atom.
General formula: -SH
Also Known As: sulfanyl group, mercapto group
Examples:
The amino acid cysteine contains a thiol group.
By Anne Marie Helmenstine, Ph.D., About.com Guide
This is the chemical structure of cysteine. The yellow SH on the left hand side is a thiol group.
Todd Helmenstine