Constituency is an area whose voters elect a representative to a legislative body.
India is divided into different areas for the purpose of elections. These areas are called electoral constituencies. The voters living in an area elect one representative.
For Lok Sabha elections, India is divided into 543 constituencies. The representative elected from each constituency is called a Member of Parliament or an MP.
Each state is divided into a specific number of Assembly constituencies. In this case, the elected representative is called the Member of Legislative Assembly or an MLA.
Each Parliamentary constituency has within it several assembly constituencies.