Science is essential knowledge. The word 'science' is derived from the Latin word 'scientia' which means "knowledge". But science is a particular kind of knowledge,that is , knowledge that has been obtained through the "scientific method".
In a more general sense , science refers to "any systematic study of physical or social phenomena"
In a more restricted sense, science can be understood as "the study of physical and social phenomena where this involves observation,experiment,appropriate quantification and the search for universal general laws andexplanations.
From a sociological stand point,"science is a body of knowledge about the natural world and a method for discovering such knowledge and a social institution organised around both".
In simple words , "science is a systematic body of knowledge".