A style of composition centred around complex counterpoint, used in the 16th-18th centuries. The word 'ricercar' is derived from the Italian 'ricercàre', literally meaning 'to seek out'. The Oxford Companion to Music says of ricercar form: '...a composition in the fugue style using the most elaborate contrivances of counterpoint, all variations of canonic writing, augmentation, diminution, inversion, etc.', but other sources claim that the ricercar is simply one of a class of polyphonic compositions taking the characteristics of the old vocal motets into instrumental music.
Bach featured two ricercars in his Musikalisches Opfer - one using three voices and a slower one using six. Interestingly, Bach dedicated his Musical Offering with the Latin inscription Regis Iussu Cantio Et Reliqua Canonica Arte Resoluta1 -- the letters of which spell out ricercar.
1"By order of the king, the air and the remainder are treated according to the art of the canon."