[abdullahkhalids]

> Are mathematicians ever frustrated that they don't understand what the variables mean?

Yes, if the presenter does not define them, or if the variables don't have a "usual" definition within the field.

> But would you have been able to tell what "b" meant without someone telling you?

Probably not.

Mathematicians, being humans, are not perfect by any means. They will sometimes fail to define things properly. But they are not stupid - they do have a cultural norm of defining everything, that is obeyed most of the time. Conversely, readers of mathematics are not perfect either. They will sometimes skip over the definitional part of a paper/book and jump straight to the results, and wonder why they can't understand.