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.

Another question is how to gain financial use from it? And What is more important - humans' curiosity or financial profit?