The dictionary definition of science is knowledge; from Old French and Latin - to know - as in - knowledge obtained by study and practice. Any department of systematized knowledge,and any branch of study concerned with observation and classification of facts, especially with the establishment of veritable general laws, chiefly by inductive logic and hypothesis - as mathematical science.
Also, science is accumulated knowledge systematized and formulated with reference to the discovery of general truths or the operation of general laws; especially such knowledge when it relates to the physical world - called also natural science.
The means by which all of this is done is called 'the scientific method', and is based upon The Laboratory Experiment. This is much further explained farther along ...