Uncertainty -

• Quantified statement regarding the possible errors incorporated into a measurement as a result of the ability to accurately measure the indirect measurement factors. When reported with a specific measurement , the value is numerical.

• For quick overview, see "On Measurement Uncertainty" by Dr. Jim Salisbury
  (Used by permission Dec 2001)

• See NIST web pages: 
•  Guide to expressing uncertainty (GUM),
• (GUM) PDF document,
• glossary on uncertainty