music with no tonal center or sense of key.      

Example: No. 18, "Der Monfleck" and no. 21, "O alter Duft aus Märchenzeit" from "Pierrot lunaire" by Schoenberg

a multi-movement work written for orchestra and soloist(s). It is meant to showcase the virtuosity of the soloist(s).

Example: Violin Concerto in E Minor, op. 64 by Felix Mendelssohn