full width of the browser and automatically resized according to the size of the browser window i.e. no fixed width. in this we do not mentioned CSS Width property like width: 180px OR WIDTH: 100% ;
This type of width we generally use for fluid layout design
It is fixed width and can not resized automatically as fluid like width: 180px ;
while writing CSS generally use either percentage widths or fixed widths.
This type of width we generally use for fixed layout design