Shirts are made from oxford cloth, but usually shirting fabrics are a bit finer weave, more similar to quilting cotton. It can be the same weight as quilting cotton, or a bit lighter. Think a dress shirt. Often people will refer to shirting fabric because of the print. Stripes, plaids or very small motifs usually in a pale single color on a light background.
Like this:
http://www.oldsouthfabrics.com/shop/...1-x5563811.htm