A "phase" in an electrical system is often referred to as the waveform (may be voltage or the current) of the power supply.
The waveform in an AC system is typically bipolar symmetrical sine wave and it varies periodically with time.
In a single phase AC system ,there are two conductors. One of the conductor is the supply (often called as the "Live" or "Phase" ) and another conductor is a return path (called as "Neutral"). The operating voltage and frequency of the AC system may be 230V,50 Hz or 110V,60 HZ respectively (depending on the region)
Single phase supply is generally used for domestic household or commercial supplies and street lighting. Industrial supplies requires three phase electrical supply .