Coats, jackets and blazers are all part of the same clothing family with few differences.
Blazer: Blazer is an all-season garment and is made of light and breathable material. It has replaced a suit as the preferred formal wear. A blazer can also be paired with a T-shirt and sneakers for a casual smart look.
Suit: Suit is a full formal set with trousers and jacket (two-piece) and sometimes also a waistcoat (three-piece). It is a formal outfit, and the entire set is made from the same fabric.
Coat: Coat is an outer garment worn over clothes primarily in winters to keep warm. It is made of fabrics like wool, fur, leather and suede. It can be paired with any outfit.