The ISM Services Purchasing Managers' Index (PMI) is an economic indicator that measures the activity and health of the services sector. It provides insights into factors such as business activity, new orders, employment, and supplier deliveries. A PMI above 50 indicates expansion in the services sector, while a reading below 50 suggests contraction. The ISM Services PMI is used to gauge the overall economic conditions and sentiment in the services industry, which is a significant driver of economic growth and employment.