The Local Meridian is the great circle running from the North point of the horizon through the zenith and to the South point of the horizon. This meridian is very important in time measurements. Azimuth is measured clockwise from the North point. Altitude is measured from the horizon to the object. Both are measured in degrees.
Local coordinates are unique for each individual observer.
As the Earth rotates on its axis, objects change their position in the sky relative to the observer. This means that the altitude and azimuth of an object change constantly. In particular, the Sun rises from an easterly direction and crosses the Local Meridian. Sunrise is defined as the time when the centre of the Sun is on the horizon while it is moving above the horizon. Local Solar Noon is the time when the Sun's centre is on the Meridian.