The standard deviation of the responses about the population line is the same for all values of the explanatory variable.

I understand this as:

If X has a certain value the mean value of Y for that X value has a certain standard deviation. That standard deviation of Y is equal for all X values.

I have two questions about that:

1. Do i interpret the first statement correctly?

2. If so, should the standard deviation be exactly the same or is it allowed to differ slightly?

I am sorry if this is a stupid question but i couldnt find it on the internet.

Thank you in advance