Police actually does not have any full form, but some people have given their own full forms to them according to their work, like :
POLICE - Polite Obedient Loyal Intelligent Courageous Efficient
POLICE - Protection of Life in Civil Establishment
They are government officials who look for the safety and health of the citizen. Their tasks is to prevent or detect crimes (if already happened), enforce laws to make country's homes and streets crime free. Their work is very diversified and depends upon the exact position in which the police officer is employed.
They usually work during days, nights, on holidays, events and even on some festivals. Some officials has the task of patrolling during day and night, i.e. to check the status of all the roads and areas and look out for any crime or mishap.