[NTG-context] defining (new) macros with optional arguments

Hi, Does something like \newcommand exist in ConTeXt? My questions aims especially at the optional argument with a predefined value. So, how do I realize \newcommand{\test}[2][A]{foo} with ConTeXt. In the fine manual I found an index entry \definecommand, but in the 'rest' of the manual it was never mentioned (print and screen version alike)! Regards, Juergen