A recursive relationship can be defined as A relationship that is expressed about multiple records within one table. As an example if we take an employee table then there are some employees who are supervisor and some who are being supervised. This is the relationship of Supervisor and supervisee is called a recursive relationship.

More concrete definition of Recursive relationship can be A relationship between information held in a field, group of fields, or complete record and information of the same type held in one or more other occurrences of that record, or part thereof.

Thanks and hope this clears things out.
Shabbir Bhiman