In fashion design, "boyfriend" is a style of women's clothing that draws heavily from corresponding men's garments. Boyfriend-style clothes are designed to be looser or boxier and tend to be oversized  giving the appearance that one is wearing their boyfriend's clothing.

To sum up, there are numerous differences in the construction of the garment and, therefore, in the final result. For instance, the jacket has rounder, more structured shoulders, whereas the blazer is closer to the style of a unstructured jacket: simple, with softer shoulders and a relaxed fit.