In common usage, the terms "mildew" and "mold" are for the most part interchangeable. In some cases they are used in the same phrase: "mold and mildew". The terms are used to describe the physical appearance of common fungi seen growing on objects both inside and outside buildings. This includes solid surfaces such as walls, floors, ceilings, as well as fruits and vegetables (fruits and vegetables are usually referred to as "moldy"). Mold growing on a shower curtain or bathtub is generally referred to as "mildew" (note the contextual use of the term).
Mildew is a term also used by plant scientists to describe plant diseases such as powdery mildew of roses and lilac. There is a difference between the scientific use of the word mildew as it applies to plant pathology and mildew in buildings and on clothing.
Mildew on clothing may be and often includes the same mold types that that grow on building materials that we might describe as moldy. Note mildew is commonly used to describe fungal or mold growth in bathrooms and clothing. It is usually a distinction without a difference.