I once took a psychology course where the professor pointed out that the word "discrimination" can be more broad than the way it is generally used. For example, it can be considered discrimination that only people above a certain height are hired as firefighters. Athletes may not make the team because they can't lift a certain amount etc.
What exactly counts as illegal discrimination? For example, I know a person can't be refused service due to their race or skin color.
In particular, I'm wondering about discrimination against students. There was a sign posted on a store saying, "only 3 students allowed in at a time". I've heard that was illegal as it presupposes students are thieves.