Mountain time 
noun [mass noun]
The standard time in a zone including parts of Canada and the US in or near the Rocky Mountains, specifically:
- (Mountain Standard Time abbreviation MST) Standard time based on the mean solar time at the meridian 105° W., seven hours behind GMT. (Mountain Daylight Time abbreviation MDT) Mountain time during daylight saving, six hours behind GMT..
- The same line separates the Pacific and Mountain time zones - and Arizona doesn't observe Daylight Saving Time.
- This is similar to much of Texas, which should (by longitude) be mostly in the Mountain time zone instead of the Central time zone.