The word science comes from the Latin "scientia," meaning knowledge.

How do we define science? According to Webster's New Collegiate Dictionary, the definition of science is "knowledge attained through study or practice," or "knowledge covering general truths of the operation of general laws, esp. as obtained and tested through scientific method [and] concerned with the physical world."

What does that really mean? Science refers to a system of acquiring knowledge. This system uses observation and experimentation to describe and explain natural phenomena. The term science also refers to the organized body of knowledge people have gained using that system. Less formally, the word science often describes any systematic field of study or the knowledge gained from it.

What is the purpose of science? Perhaps the most general description is that the purpose of science is to produce useful models of reality.

Most scientific investigations use some form of the scientific method. You can find out more about the scientific method here.

SCIENCE is

Knowledge, especially that gained through experience. And the organized body of knowledge gained through such research.

It is a "systematic enterprise of gathering knowledge about the world and organizing and condensing that knowledge into testable laws and theories".

science [Lat. scientia=knowledge]. For many the term science refers to the organized body of knowledge concerning the physical world, both animate and inanimate, but a proper definition would also have to include the attitudes and methods through which this body of knowledge is formed; thus, a science is both a particular kind of activity and also the results of that activity.

Science (from the Latin scientia, meaning "knowledge") is, in its broadest sense, any systematic knowledge that is capable of resulting in a correct prediction or reliable outcome. In this sense, science may refer to a highly skilled technique, technology, or practice.

Scientific fields are commonly divided into two major groups: 

Science as defined above is sometimes called pure science to differentiate it from applied science, which is the application of research to human needs. Fields of science are commonly classified along two major lines:     - Natural sciences, the study of the natural world, and     - Social sciences, the systematic study of human behavior and society.

Natural sciences:

A science, such as biology, chemistry, or physics, that deals with the objects, phenomena, or laws of nature and the physical world. (Dictionary)

In science, the term natural science refers to a naturalistic approach to the study of the universe, which is understood as obeying rules or laws of natural origin.

social sciences:

Any discipline or branch of science that deals with the sociocultural aspects of human behaviour. The social sciences generally include cultural anthropology, economics, political science, sociology, criminology, and social psychology. Comparative law and comparative religion (the comparative study of the legal systems and religions of different nations and cultures) are also sometimes regarded as social sciences. (Britannica Encyclopedia)

The study of human society and of individual relationships in and to society. A scholarly or scientific discipline that deals with such study, generally regarded as including sociology, psychology, anthropology, economics, political science, and history. (Dictionary)

Social science, term for any or all of the branches of study that deal with humans in their social relations. Often these studies are referred to in the plural as the social sciences. Although human social behavior has been studied since antiquity, the modern social sciences as disciplines rooted in the scientific method date only from the 18th cent. Enlightenment. Interest at first centered on economics, but by the 19th cent. separate disciplines had been developed in anthropology, political science, psychology, and sociology. The 19th cent. was characterized by the development of wide-ranging theories (e.g., the work of Auguste Comte, Karl Marx, and Herbert Spencer). Developments in the 20th cent. have moved in these directions: the improvement and increased use of quantitative methods and statistical techniques; increased use of the empirical method, as opposed to general theorizing; and the direct practical application of social science knowledge. Social science departments are now firmly established in universities, and social scientists are increasingly called upon to advise industries and governments for future planning (Columbia encyclopedia)