A blazer is a type of jacket resembling a suit jacket, but cut more casually. A blazer is generally distinguished from a sport coat as a more formal garment and tailored from solid colour fabrics. Blazers often have naval-style metal buttons to reflect their origin as jackets worn by boating club members.
A blazer is a wildcard, it can be worn both in casual contexts and in casual business meetings. It's less formal than a classical suit jacket, and the perfect companion for your weekend activities, because it has a casual elegance that's inappropriate on formal business occasions.