CSAT (Customer Satisfaction Score) is a tool that measures customer satisfaction from the recent interaction. Typically it can be a service or a product a customer has bought. CSAT survey question could then be, for example:
How satisfied were you with the product/service you received?
CSAT focuses to measure customer satisfaction in s shorter term so it does not predict customers' future behavior. Also, CSAT score is usually supporting NPS survey results and is thus not competing with NPS. CSAT surveys also enable to contact customers if they are very dissatisfied with a product/service since the tool provides specific information of service quality.