If software behaves in an identical way for a set of value, then the set is termed as equivalence class or a partition. It can be assumed safely that functionality of the software will be same for any data value from the equivalence class or partition. In equivalence partitioning, input data is analyzed and divided into equivalence classes which produces different output. Now, data from these classes can be representative of all the input values that your software expect. For equivalence classes, it can be assumed that software will behave in exactly same way for any data value from the same partition.
