Especially an army, but more commonly now in general, with the connotation of things that hinder more than help. In comedy routines, the pile of stuff carried by the go-fer. All the electronic devices that you don't quite have enough pockets for. The one too many bags of groceries you bring in. Those parts of a teenager's room that do not have trails. The things that impede -- which is indeed the source: borrowed in the 1590s from the Latin, the plural of impedīmentum, impediment (which comes from that singular form), from impedīre, to entangle, lit. snare the feet (from which comes impede), from im- + ped + verbal ending. An example from a military memoir by Frances Isabella Locke "Mrs. Henry" Duberly:
Thanks to the kindness of Captain Buckley, of the Scots 'Fusileer Guards, and Colonel Somerset, who lent us means of conveyance for our impedimenta, I was able to move up in one day.