Hive query execution issue

When executing a hive query, here is the output, wondering for "Map 1" and "Reducer 2", what does the 1 and 2 mean?

Map 1: 21/27    Reducer 2: 0/1
Map 1: 22/27    Reducer 2: 0/1
Map 1: 23/27    Reducer 2: 0/1
Map 1: 24/27    Reducer 2: 0/1
Map 1: 26/27    Reducer 2: 0/1
Map 1: 27/27    Reducer 2: 0/1
Map 1: 27/27    Reducer 2: 1/1

thanks in advance, Lin