What does "trainband" mean?

Trainband: A band or company of an organized military force instituted by James I. and dissolved by Charles II.; -- afterwards applied to the London militia. [Eng.] He felt that, without some better protection than that of the trainbands and Beefeaters, his palace and person would hardly be secure. Macaulay. A trainband captain eke was he Of famous London town. Cowper.