Accuracy and precision are two measures of observational error:
In the language of statistics:
In the context of observations made on a ratio or interval scale, a statistical sample can be said to be accurate if its average is close to the true value of the quantity being measured and precise if its standard deviation is small.
See Terminological disambiguation below for i) other words that refer to the same concepts; and ii) the use of the words 'accuracy' and 'precision' to refer to related but different concepts.