What did segregation mean for the people of the USA?
It is hard to say exactly what segregation meant to each person in the United States without having interviews with each of those people. We simply cannot know how the typical person really felt about segregation.
In general, however, we can say that the majority of Americans were not affected by segregation in any practical way. The great majority of Americans during the era of segregation were white. White people were not really all that affected by segregation in practical ways because they were not denied access to anything that they really wanted. They were not made to feel like second class citizens. What is more, many white people lived in the North where there was no segregation and where (at least in many places) there were hardly any African Americans. Segregation did not affect them in any real way.
Of course, segregation did mean something to African Americans. It meant that they were treated as lesser human beings. It meant that they had to feel oppressed wherever they went. This was very important because of how painful it was to them.
We can also argue that segregation affected all Americans by making them live in a country that allowed injustice. However, this probably had very little meaning to the average American at that time. Therefore, we can say that segregation had no practical meaning to the average American.