Political parties nominate their candidates to each constituency. All the people residing in that constituency who has completed 18 years of age cast their vote.

A constituency means the body of citizens eligible to vote for a particular representative. 

(OR) 

A country is divided into many separate units or areas for the purpose of holding elections. Each area in which elections are held is known as a constituency. People living in a consti-tuency elect their own representative from their constituency.