Clothes worn in daily life, as opposed to formal wear, uniforms, or special-occasion outfits.
On my days off, I often spend the day in casual clothes.
It's rude to go to a party in your everyday clothes.
I went to the neighborhood supermarket in casual clothes.
I came home from work and immediately changed into casual clothes.
普段着 means ordinary, everyday clothes, the opposite of the elegant special-occasion attire implied by 盛装.
arrival at ... · counter for suits of clothing · nth place (in a race) · counter for moves (in go)