A garment made from an inexpensive fabric such as muslin or calico, usually without seam finishes, facings or closures, for the sole purpose of fitting.
As different patterns react differently to different fabrics, toiles are not always made from calico or muslin. The general rule is that the toile should be made of a fabric that drapes similarly to the fabric that the final garment is made of.
For the purpose of making your own blocks and testing their fit, calico and muslin are the most suitable fabrics.
Bodice Block Toile.