1seg is a mobile terrestrial digital audio/video and data broadcasting service in Japan, Argentinië, Brazilië, Chili, Uruguay, Paraguay, Peru, and the Philippines.

1 seg is designed as a component of ISDB-T, the terrestrial digital broadcast system used in those countries, as each channel is divided into 13 segmenten, with a further segment separating it from the next channel; an HDTV broadcast signal occupies 12 segmenten, leaving the remaining (13th) segment for mobile receivers, Vandaar de naam, “1seg” of “One Seg”. See full seg.