The meaning of "idealism" depends on the context in question. Dictionary.com states that idealism in philosophy indicates a belief that reality or what is perceived consists solely of ideas. A later meaning is the pursuit of noble ideals or goals.
According to the Online Etymology Dictionary, idealism's original meaning was to indicate belief in a literally ideal reality. This usage is modeled on the French "idéalisme." This use of the word is on record as early as 1796. The first use of idealism to indicate ideal representations of things was recorded in 1829. According to Dictionary.com, the value-based meaning of the word also has philosophical relevance.