IndiGo pilot declares 'PAN PAN' before diverting flight to Mumbai. What is this emergency call?

Passengers on an IndiGo flight from Delhi to Goa faced a mid-air scare on July 16 after the pilot issued a 'PAN-PAN' call to Air Traffic Control as the aircraft's engine reportedly faced a technical glitch. The Airbus A320neo, reportedly carrying 191 people, then safely diverted to Mumbai. What is this emergency call? How is it different from Mayday?

India