Final answer:
A government system where the legislative body holds power and the country's leader is part of that legislature is known as a parliamentary system.
Step-by-step explanation:
When the power lies with the legislative body, and the leader of the country is part of that legislature, the system of government is a parliamentary system. In a parliamentary system, there is a close relationship between the legislative and executive branches. The head of the executive, often called the prime minister, is chosen from within the legislature by the majority party or coalition. This system is characterized by the fusion of powers between the legislative and executive branches, with the prime minister leading the government while also being a member of the legislature.