Map comes under the data mode in pig. It is the collection or set of key value pair.Here the texts before the # are keys and texts after the # are values. In pig # is the delimiter that represents the difference in key and value pair. So, every row is a Map which has a set of key value pairs. However a Map cannot contain duplicate pairs.
For example;- [Band# Linkin Park, Member# 7, Origin# California]
Here to represent a Map you need to use the square brackets.