Calabarzon, sometimes referred to as Southern Tagalog and designated as Region IV‑A, is an administrative region in the Philippines. The region comprises five provinces: Batangas, Cavite, Laguna, Quezon, and Rizal; and one highly urbanized city, Lucena. It is the most populous region in the Philippines according to the Philippine Statistics Authority (PSA), having over 16.1 million inhabitants in 2020, and is also the country's second most densely populated after the National Capital Region. It is situated southeast of Metro Manila, and is bordered by Manila Bay and South China Sea to the west, Lamon Bay and the Bicol Region to the east, Tayabas Bay and the Sibuyan Sea to the south, and Central Luzon to the north. It is home to places like Mount Makiling near Los Baños, Laguna, and Taal Volcano in Batangas.

Tagalog is an Austronesian language spoken as a first language by the ethnic Tagalog people, who make up a quarter of the population of the Philippines, and as a second language by the majority. Its standardized form, officially named Filipino, is the national language of the Philippines, and is one of two official languages, alongside English.