An election held for only one constituency to fill the vacancy caused due to the death or resignation of a member is called a by-election. Let's break down the answer and understand the concept in detail.

Explanation:
By-elections, also known as special elections or bye-elections, are held to fill the vacancy in a single constituency in between general elections. These vacancies arise due to various reasons such as the death, resignation, or disqualification of a sitting member of the legislative body.

Key Points:
1. Definition: A by-election is an election held to fill a single vacancy in a constituency.
2. Occurrence: By-elections occur when a seat becomes vacant before the next scheduled general election.
3. Reasons for Vacancy: The seat can become vacant due to the death, resignation, disqualification, or any other reason that renders the position vacant.
4. Importance: By-elections are crucial as they ensure representation for the constituents in the affected constituency.
5. Duration: By-elections are usually conducted within a relatively short period after the vacancy occurs.
6. Procedure: The electoral process for a by-election is similar to that of a general election, with eligible voters casting their ballots to elect a new representative.
7. Candidates: Political parties and independent candidates can participate in a by-election, and voters choose their preferred candidate to fill the vacant seat.
8. Representation: By-elections help maintain the democratic functioning of the legislative body by ensuring that all constituencies have representation.

Importance:
By-elections play a significant role in maintaining the democratic process by promptly filling the vacant seats in a constituency. They provide an opportunity for constituents to choose their representative and ensure that their voices are heard in the legislative body.

Conclusion:
A by-election is held to fill a single constituency's vacancy caused by the death or resignation of a member. It is a vital democratic process that ensures representation for the affected constituents. By-elections are conducted similarly to general elections, allowing eligible voters to choose a new representative for their constituency.

By elections are held to fill the vacancy caused by the death or sudden resignation of a member.
so the answer is correct...