Midday, also referred to as noon, refers to 12 PM or 12:00 on a 24-hour clock in civil time, and is the time that is 12 hours before or after midnight. Civil time today is based on Coordinated Universal Time (UTC); areas around the world have their own standard time based on time zones that are offset from UTC.
Solar noon refers to the time at which the Sun reaches its highest point in the sky during a given day. This rarely coincides with noon in civil time since noon in civil time is based on time zones rather than on longitude and time of year.
Solar noon occurs at exactly the same point in time in all areas with the same longitude. As the Earth rotates, the longitude at which solar noon is occuring shifts from east to west; areas to the east of a given location experience solar noon earlier and areas to the west experience solar noon later.
Since the North and South Pole do not have a longitude (meridians converge at the poles), there is no solar noon at the poles. At the poles, the position of the sun constantly increases during winter and spring and decreases during summer and fall.
Noon on digital clocks
On digital clocks, noon is conventionally written as "12 PM." However, based on the Latin meaning of PM, which stands for post meridiem, which means "after midday," it is technically incorrect to use either AM or PM to indicate noon. Noon is neither before or after midday, since noon is midday. This is similar to the use of AM on digital clocks to indicate midnight as "12 AM." Midnight is exactly 12 hours before or after noon, making the use of AM or PM ambiguous.
On 24-hour clocks, midnight is indicated using "00:00" and noon is indicated using "12:00." To avoid confusion when referencing midnight on a specific day/date, it is common to use "11:59 PM" or "12:01 AM" while providing a day/date. This is particularly important when communicating schedules.