1seg is a mobile terrestrial digital audio/video and data broadcasting service in Japan, Argentino, Brazilo, Ĉilio, Urugvajo, Paragvajo, Peruo, 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 segmentoj, with a further segment separating it from the next channel; an HDTV broadcast signal occupies 12 segmentoj, leaving the remaining (13th) segment for mobile receivers, hence the name, “1seg” aŭ “unu Seg”. See full seg.