1seg is a mobile terrestrial digital audio/video and data broadcasting service in Japan, Arjantîn, Brezîlya, Şîlî, Ûrûgûay, Paraguay, Perû, 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 beşan, with a further segment separating it from the next channel; an HDTV broadcast signal occupies 12 beşan, leaving the remaining (13th) segment for mobile receivers, hence the name, “1seg” an “yek Seg”. See full seg.