Final answer:
A Pair RDD is a data structure in Apache Spark for key-value pairs that allows operations like counting occurrences of words in a text document.
Step-by-step explanation:
A Pair RDD (Resilient Distributed Dataset) is a data structure in Apache Spark that represents a collection of key-value pairs. It is a fundamental building block of Spark's distributed computing framework. Pair RDDs have additional functionality compared to regular RDDs, allowing operations specific to key-value pairs such as grouping, aggregation, and joining.
For example, you can use a Pair RDD to perform operations like counting the occurrences of each word in a text document, where the word is the key and the count is the value associated with it.