Retirement tax questions

Thanks everyone. I've obviously not done a good job of wording my question.  Or I've got a thick skull. I still don't understand deferring $25K. That I can deposit up to $45K in my individual 401(k) is clear. But the deferring? Why not just say I can put up to $45K into my 401(k)? I think what I may be missing is the "profit sharing" component that allows over $25K.

 

In any case, I appreciate everyone's efforts to assist me.