MemberApril 29, 2016 at 10:35 am
Matching rules use criteria to determine how closely a field on a new or edited record matches the same field on an existing record, and, ultimately, whether the two records are duplicates. When you create a custom matching rule, you need to define certain criteria. For standard matching rules, the criteria are already defined for you.
This link https://help.salesforce.com/apex/HTViewHelpDoc?id=matching_rule_matching_criteria.htm&language=en_US will give you a detailed description.