PDT is Pacific Daylight Time: the summer clock on the west coast of North America. Cities such as Los Angeles, San Francisco, Seattle, and Vancouver use it in the warm months, when they move the clock forward one hour. PDT sits seven hours behind Coordinated Universal Time. Though actually those same places do not keep PDT all year. In winter they switch back to Pacific Standard Time (PST), which is one hour earlier. News, flight boards, and online meetings write 5 p.m. PDT so people in other countries know which clock to follow. Taiwan does not change its clocks with the seasons, so the gap between Taipei and the American west coast is not the same in July and in January. People sometimes say Pacific Time and skip the extra letter; that extra letter is what stops you being an hour late.