Agreement is the degree to which two raters, instruments, etc, give the same value when applied to the same object. Special statistical methods have been designed for this task.

Agreement is the degree to which two raters, instruments, etc., give the same value (rating / measurement) when applied to the same object. Agreement can be assessed to determine if one measurement can be substituted for another, the reliability of a measurement, etc. Trying to assess agreement using a correlation coefficient (or perhaps a chi-squared test for categorical variables) is a very common and intuitive mistake. Special statistical methods have been designed for this task.

Some references: