Any food item is considered expired when it is not fit for human consumption or its original appearance has undergone a significant change. Example of the first, bacterial growth, rancidity and unexpected modification of chemical makeup. Example of the latter, pineapple slices in can became shredded, a hardened milk powder and a liquified instant coffee powder.
How about the non food items? When can we say that they are expired and how they got expired? Wayback, I asked my boss, a veterinarian, why the sterile syringe had an expiry date printed on label. He immediately answered. The expiry date was an indication that the syringe may not be as sterile as it was packed in the factory. Microbes and unwanted chemicals might had penetrated the paper plastic packaging.
Non food items like, disposable gloves, syringes, single use petri dishes and disposable pipettes, will not get spoiled but may become unsuitable for its intended purpose via two ways. First, accidental package break or opening but not using it immediately. It allows the rapid entry of unwanted microbes, chemicals and other debris. Second, natural product degradation. Disposable gloves, plastic petri dishes become brittle on storage. Hot and moist conditions shorten the expected usable life.