DoE, RSM: What does Factor A*Factor A mean?

#1
Hello everyone,

For my thesis I have to make an optimization using DoE. Most of it is clear to me now, but there is one thing which i don't quite understand (see attachment, red circles). What is the difference between A and A*A? If anyone could help me with this I'd be greatful!

Thank you in advance
 
#3
Okay, thanks. But what does it mean in the table for significance of factors. Because Factor A is significant, but A*A is not. I don't understand how they are related to eachother in that way