The CSS layout type.
A fixed width layout is one where the width is set to a specific value that is independent of the size of the client window. Layout content will not be adjusted as the window is resized.
A fluid width layout is one where the layout content adjusts itself to fit the width of the client window. For example, a 100% width fluid layout will take up the entire width without producing a scroll bar. It will only produce a scroll bar when resized to a small window.
Fixed for the 1 column layout and Fluid for the 2 and 3 column layouts.
Fixed or Fluid.