The Full form of SP is Superintendent of Police. In India, a Senior SP (Superintendent of Police) in highly populated, metropolitan, or naxal-effected districts or SP in smaller districts heads the police force of a district. In districts where a Senior SP is the head, the SP is the head of a large rural or urban area within a district. The SP is also the head of a large rural or urban area in a smaller district as well.
In metropolitan cities having police commissioner-ate system (like in Mumbai Police, Delhi Police, or Hyderabad Police) the head of district police is called DCP (Deputy Commissioner of Police), and he or she holds the rank of a Superintendent. SP-ranked IPS officers wear the IPS (Indian Police Service) logo below the Star/Ashoka emblem and SP-ranked state police service officers wear the state police (e.g. Haryana Police, Punjab Police, Maharashtra Police etc.) logo below the star/Ashoka emblem. So, SPs (Superintendents of Police) are the officers of either Indian Police Service or State Police Service.
In India, they are the district heads of non-metropolitan districts. They also serve as assisting officers to the ADGP (Additional/Special Director General of Police) in various bureaus. In the State Police Service, the rank below SP is deputy superintendent or assistant superintendent of police in the IPS and the rank above SP is senior superintendent.