First Mass refers to the first occasion a Eucharistic celebration (a Mass) takes place. There are two natural contexts to its use: Historical, which would be the first occasion where a Mass is celebrated in a particular place, such as the First Mass in the Philippines.
In my opinion, I believe that the first Mass occurred in Masao in Butuan, Agusan del Norte. Historically, Mazaua was 15 leagues, roughly 45 nautical miles (83 km), below Butuan in 1521, which in Pigafetta's map and text is a more extensive geographical conception than the present-day map. Further, the distance to Cebu from Mazaua, according to Pigafetta, was 35 leagues (140 miles). The distance from Limasawa to Cebu is only 80 miles. Thirdly, American historians Emma Helen Blair and John Alexander Robertson claimed in 1909 that the island of Mazaua is the present island of Limasawa without giving any explanation for the identification, thus justifying it was Masao. Historians have been heard saying, "It is high time for contemporary historians and the Philippine government to correct their mistake and accept that the first Christian Mass was celebrated in Masao, Butuan, Agusan del Norte, and not. Limasawa, Leyte, on Easter Sunday, March 31, 1521.”