1. The offset of one's waking-sleeping schedule with respect to the standard 24-hour cycle; a useful concept among people who often work at night and/or according to no fixed schedule. It is not uncommon to change one's phase by as much as 6 hours per day on a regular basis. "What's your phase?" "I've been getting in about 8 P.M. lately, but I'm going to wrap around to the day schedule by Friday." A person who is roughly 12 hours out of phase is sometimes said to be in "night mode". (The term "day mode" is also (but less frequently) used, meaning you're working 9 to 5 (or, more likely, 10 to 6).) The act of altering one's cycle is called "changing phase"; "phase shifting" has also been recently reported from Caltech. 2. "change phase the hard way": To stay awake for a very long time in order to get into a different phase. 3. "change phase the easy way": To stay asleep, etc. However, some claim that either staying awake longer or sleeping longer is easy, and that it is *shortening* your day or night that is really hard (see wrap around). The "jet lag" that afflicts travelers who cross many time-zone boundaries may be attributed to two distinct causes: the strain of travel per se, and the strain of changing phase. Hackers who suddenly find that they must change phase drastically in a short period of time, particularly the hard way, experience something very like jet lag without travelling.

In wave motion, oscillating motion, simple harmonic motion, or similar periodic phenomena, the interval of time passed from the time the moving particle moved through the middle point of its course to the instant when the phase is to be stated.