Circa- meaning "approximate" and often abbreviated to ca. It is used in instances where the exact date is not known, such as in pieces and composers from the Middle Ages.
Form- the structure in which music is created. common forms include binary, ternary, strophic, through-composed, sonata-allegro, etc..
Impresario- an entertainment promoter, manager or owner who books and staages public, usually music or theatre, Seigei Diaghilev of Les Ballets Russes is one of the best-known 'impresarios' of the 20th century.
Instrumentation - also called " orchestration", it is the art of arranging a composition for performance by an instrumental ensemble. this is often referred to as scoring the composition.
Kapellmeister _ German for 'music director', the term is often used when describing the musical post of composers such as Handel and Haydn.
Modulation - when music changes from one key to another.
Opus - the Latin word for 'work'
Sacred comes from the Latin word sacer, meaning 'holy'.
Secular - in music, it refers to non-religious works.
Synopsis - in music, it generally means a summary of a libretto or other text.