A scientist is anyone who engages in the pursuit of scientific knowledge, which is concerned with understanding the laws that make up the physical universe. The practice of science rigorously attends to unbiased observation and robust experimentation.
There are many kinds of scientists, corresponding to a wide variety of branches of the various scientific disciplines, like physical science, Earth science, biology, medicine, engineering and social science. Scientists study a wide variety of subjects. For example, some scientists may study the laws of nature that govern the extra-terrestrial phenomena that occurs in outer space. These scientists are usually referred to as astronomers.
Some scientists study theories and disciplines that are highly theoretical, like quantum physicists. These kinds of scientists primarily attempt to explain the physical laws that make up the physical world, focusing specifically on the very smallest pieces of matter and energy that make up the universe. Other scientists, like engineers, work towards applying science to more tangible dimensions, like the building of bridges and power systems.
Scientists follow their own philosophy or methodology, usually referred to as the scientific method. Science isn't just an academic pursuit, there are numerous contexts where science is used in practical applications, like industrial and commercial settings and even instances of political action.