The mens blazer is by definition an odd jacket, or a jacket that has been cut separately without a matching pair of trousers, clearly differentiating it from a suit. The blazer is a great way to add a whole new range of outfits by pairing them with anything from a pair of jeans to a different colored trouser like the gentleman has done on the right.
The great versatility of the mens blazer really shines when you have to go to more than one place in a day and don’t feel like running home to change. You can wear a blazer with gray trousers and a tie to work, and then remove the tie and throw on some jeans for a dinner date in the city.