/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/Metadata.framework/Versions/A/Support/corespotlightd corespotlightd is a daemon responsible for Spotlight indexing so that users can search content on Mac. For example, corespotlightd is running when you press Command + Space to search for something or enter a query in the search box of the Mail app.
The binary is a part of CoreServices public framework.