Pig is a component which abstracts the map-reduce programming by the way of providing the simpler SQL like language called Pig Latin. Pig translate Pig Latin into map-reduce underneath.
Though Pig has largely been replaced with other components such as Hive and Spark, still learning pig can help you understand the distributed computing and lazy evaluation. Also, in many organizations, Pig is still being used.
This chapter will give you a good insight into interacting with Pig and writing Pig Latin.