Sexism, racism, ageism, discrimination towards disabled people - I’m sure that every person who has worked in a team has experienced discriminating attitude based on at least one of these factors. I’ve witnessed it even in the companies that positioned themselves as open to diversity and standing for inclusion. One of such companies was placed in a separate three-floor building without any (none, zero) ramps. This is a kind of an indirect discrimination towards people with disability because such people cannot physically reach a potential workplace.
Another company that was praising the equality and inclusion has organized a team-building picnic in the middle of the suburban resort setting in the highlands. As you see, for the people on wheelchairs it was also impossible to join.
On the other hand, there is a direct demonstration of prejudices when top-management positions are occupied only by people over 50 years of age. Or, on the contrary, there are age limits for an employment. When there is a dress code for women according to which they must be wearing makeup - it’s a sexism (more about a sexism at a workplace you can read in this paper). There are, of course, some vulgar demonstration of xenophobia when people with AIDS got fired with no other reason except their illness. On this topic, there is an old but beautiful film Philadelphia with Tom Hanks starring. When you see the requirement for a personal assistant position saying ‘Young, good looking woman’ - it’s also a clear sexism.
Why is sexism important to notice? Because innocent jokes and some limited views on women's rights and abilities can turn into direct sexism when women get lower wage than a man on the same positions. In most of the countries, it is a stable statistic according to which up to 90% of managerial posts belong to men. And that what a direct discrimination is about.
There are a lot of research papers discussing a discrimination at a workplace in a more precise way.