You're right that an inhalant is something that is inhaled. An inhaler, itself, is a device that delivers medication--medication that is inhaled. The medication is actually the inhalant, which is delivered through the inhaler. So in a strict sense, the inhaler, itself, is NOT a drug, but the inhalant that it delivers it IS a drug. To be practical, though, it wouldn't make much sense to carry around an inhaler with no medication inside, so when most people talk about inhalers, they're talking about both the inhaler and the medication. Confusing, isn't it?

Actually, the inhaler is a delivery tool. What it delivers is a drug. It’s like a hypodermic needle in that it is a way to get drugs into the body, but it is not a drug itself.

Some drugs have to be injected into the body in order to get into the blood, then they travel to the place they are needed. Inhalers deliver drugs right to the air passages. If the drug is for asthma, it can immediately work on the air passages to make it easier to breathe. This works because the tissues of the lungs are already specialized to allow gases to pass through them easily.

Why would it be better to have an inhalant drug than an injectable drug or a pill for asthma attacks?

Definitely. For example, delivering short- and long-acting drugs to the lungs for treatment of asthma is done through the use of inhalers.

Inhalants are usually drugs. It is possible to inhale some very simple compounds that do things to your physiology and are important under odd situations, but I'm having a hard time thinking of them.

All of this said, I'm not a doctor.