Ablism would be something like planning a company outing, and choosing the location up a tall, steep hill when other options were available, specifically because you don’t like the fact that your coworker has asthma.

It doesn’t have to be deliberately malicious to be ableism. It’s often just thoughtlessness.

The social model of disability distinguishes between ‘impairment’, which is some functional limitation, and ‘disability’ which is created by barriers to people with an impairment. Most of those barriers exist because their designers just didn’t think about it and/or were not required to. The building with steps and no ramps, the information provided by written sign only, the flashing lights which can trigger seizures. They’re not (usually) a product of irrational hate, just ignorance and carelessness, and in some cases a conscious refusal to cater for a minority need because of costs or aesthetics.

The effect on disabled people is much the same, whether it was deliberate or careless, of course.