Introduction:
The term "Apex court" refers to the highest court in a country or jurisdiction. It is the court of last resort, where the final appeals can be made and the highest level of justice is administered. In India, the Apex court is the Supreme Court.

Explanation:
India has a well-defined judicial system with a hierarchy of courts. The Supreme Court is the highest judicial body in the country and is often referred to as the Apex court. Here's a detailed explanation of why the Supreme Court is known as the Apex court:

1. District Court:
- The District Court is the lowest level of the judiciary in India.
- It is the primary court for civil and criminal cases at the district level.
- The District Court is not referred to as the Apex court because it is at the bottom of the judicial hierarchy.

2. High Court:
- High Courts are the intermediate courts in the Indian judicial system.
- Each state or union territory in India has its own High Court.
- High Courts have the power of superintendence over all subordinate courts within their jurisdiction.
- While High Courts have significant authority, they are not considered the Apex court because there is a higher court above them.

3. Gram Panchayat:
- Gram Panchayat refers to the village-level local self-government institution in India.
- It is responsible for the administration and development of rural areas.
- Gram Panchayats are not courts of law and do not have the jurisdiction to hear and decide legal disputes.
- Therefore, Gram Panchayat is not known as the Apex court.

4. Supreme Court:
- The Supreme Court of India is the highest court in the country.
- It is the final court of appeal and has the power of judicial review.
- The Supreme Court has the authority to interpret the Constitution and ensure the rule of law.
- It hears appeals from High Courts and other subordinate courts.
- Due to its highest position in the judicial hierarchy, the Supreme Court is known as the Apex court.

Conclusion:
Among the given options, the Supreme Court is the only one referred to as the Apex court. It is the highest judicial body in India and holds significant authority in interpreting and enforcing the law. The District Court, High Court, and Gram Panchayat do not have the same level of authority and are not considered the Apex court.