Racism is believing another race or races is inferior. Acting on this means direct discrimination, not taking them as tenants or staff, or paying them less. Extremes would be direct attacks, physical or verbal, and now in Britain all covered by discrimination laws.
Outside that not wanting immigration, thinking different cultures do not naturally mix, or any other preference to be with your own people is something inbuilt in all of us, as you see when looking at immigrant communities who tend to relocate a similar as possible replica of where they were to wherever they are should there be enough to do so. This extends to many locals and immigrants alike disapproving of relationships with the others, which could be considered racist as is based on a belief the other people are not good enough to associate with yours. But this attitude is equally shared between both the local people and the immigrants, if not more so by the immigrants who in some cases will ostracise or even kill the family member who mixes with the natives.
Calling people racist who do not discriminate against other races, or believe they are inferior is slander. I'm sure most people who do it know the difference perfectly well, but prefer to demean their perceived enemy of a civilised society who disagree with their policies of diversity and multiculturalism, which includes cultures coming from countries with no sewage system or have such tight communities many will never even learn English as everything they need comes from within their own groups. You can easily import as many willing economic migrants from places earning a tenth as much as here, if they can find work at all, and move from shanty towns to council and subsidised housing, but they won't mix with you except on the fringes, no more than you would if you went to one of theirs in similar numbers.
Tribalism and national and local cultures are an essential part of history and humanity. Trying to claim it is all empty and meaningless is clearly an insult to humanity, so they need to use insults to try and implement it.