Standard time is the synchronisation of clocks within a geographical area to a single standard time, rather than using solar time or a locally chosen meridian (longitude) to establish a local mean time standard.
A country may have many longitudes running across it and there is a time gap of 4 minutes between each longitude.
Example
The time gap between the western point of Gujarat and the easternmost point of Arunachal Pradesh has a time gap of 2 hours. So, there is a lot of confusion in the whole country. Therefore, a standard meridian should be established in each country as it is the central longitude of the whole country so that there is an equal time in all the country.
The purpose of Standard Meridian