can anybody tell me the meaning of the "major line every 5" come when we are in drafting setting dialog box.thanks 

This only applies if you are working in 3D, where your grid is made up of lines. Every 5th line in the grid will be bold. If you are working in 2D, your grid will be made up of dots, so the "major line every 5" does not apply.

Thank you very much sir for reply .