Answer 1

The closeness of agreement between an observed value and an accepted reference value. Also see Precision

Answer 2

1. The degree to which an indicated value matches the actual value of a measured variable. 2. In process instrumentation, degree of conformity of an indicated value to a recognized accepted standard value, or ideal value.

Answer 3

Of a measurement, closeness to the real value. "Bias" is the distance from the true value.