Warm & Natural is a brand name of one of The Warm Company (Seattle WA) products. It is a very popular low/medium-loft quilt batting.
That particular offer is for 45 inch wide bolt goods, by the bolt, the bolt containing 40 yards length. It would be good if you're re-selling, or doing a lot of small quilts (under about 40 inches wide), or don't mind piecing your batting.
Scrim is a very light material, a bit like gauze, that is used to bind the batting together and is used along with a bonding agent to make many non-woven battings. The 4 ounces refers to the weight per square yard of the batting, to give you a relative idea as to how heavy/thick the material is.
HTH.