The term conceptual art was first used to reference this distinct movement in an article written by Sol LeWitt in 1967:

In conceptual art the idea or concept is the most important aspect of the work. When an artist uses a conceptual form of art, it means that all of the planning and decisions are made beforehand and the execution is a perfunctory affair.
LeWitt, ‘Paragraphs on Conceptual Art’, Artforum Vol.5, no. 10, Summer 1967, pp. 79-83

In 1973 a pioneering record of the early years of the movement appeared in the form of a book, Six Years, by the American critic Lucy Lippard. The ‘six years’ were 1966–72. The long subtitle of the book referred to ‘so-called conceptual or information or idea art’.

http://www.tate.org.uk/art/art-terms/c/conceptual-art

Conceptual art is art for which the idea (or concept) behind the work is more important than the finished art object. It emerged as an art movement in the 1960s and the term usually refers to art made from the mid-1960s to the mid-1970s.