Final answer:
In garments, 'lining' refers to the inner layer of material that serves purposes such as warmth, comfort, or aesthetic appeal. It is the fabric covering the inside surface of a jacket or other clothing article.
Step-by-step explanation:
The term 'lining' in the context of clothing refers to a layer of material that is used to cover the inner surface of a garment. The lining can serve various purposes such as providing extra warmth, a smooth surface for comfort, or simply for aesthetic appeal with a contrasting color or pattern. In the specific context of your husband's dark brown jacket with a bright blue inner lining, the lining is the material that lines the inside of the jacket, typically the part that touches the skin or another layer of clothing.