What is the main body of the legislative branch

Answer: legislature. Legislature = deputies/representatives and senators who get elected in what is usually called legislative elections. Who votes is a population of given country (electorate).

Explanation: federations usually have bicameral systems (congress in USA, Bundestag in Germany, Congresso in Brazil) which means that the legislature has two chambers. In American case house of representatives (chamber no. 1) represents electors/electorate whereas senate (chamber no. 2) represents federative units (states) = each state 2 senators regardless of the extension of the state or number of inhabitants.