It took a little digging, but I finally understand this. PDT means "Pacific Daylight Time". It's just the time zone for the Pacific Coast. Say if you live in San Diego, CA, and the time is 10:00 A.M. PDT, then it is 10:00 A.M. In all of California and the rest of the PDT time zone. PST, which standards for "Pacific Standard Time", which as a term we use more often, is the SAME time zone. The exact same. However, you only use PST from the end of Daylight-Savings Time to the beginning of Daylight Savings Time. Therefore, during Daylight-Savings Time, you us PDT (Pacific Daylight Time). In 2009, Daylight-Savings Time began March 8th at 2:00 A.M. And will last until November 1st at 2:00 A.M, during which use us PDT. In most states in the USA and in most provinces in Canada, Daylight-Saving Time is observed. During Daylight-Savings Time, PDT is 7 hours behind Greenwich Mean Time (GMT-7). After the Summer months Pacific Time is shifted back by 1 hour to U.S. PST or (GMT-8). Greenwich Mean Time is how we measure time zones and refers to the Greenwich Meridian.
