Elemental calcium is a term that is in common use in the context of dietary supplements. Calcium is an element and is a metal, so it is reasonable to expect "elemental calcium" to refer to pure calcium metal. In the nutritional supplements business it does not.
In the nutritional supplements business, the term "elemental calcium" refers simply to calcium. If you are told you require 1 gram of elemental calcium per day that means you require 1 gram of calcium per day. This will not be calcium metal, as the name elemental calcium would lead one to think. It will be in the form of a calcium compound, typically calcium carbonate. Calcium carbonate is 40% calcium by weight, thus a 500 mg pill of calcium carbonate contains 200 mg of calcium and the container will indicate each pill has 200 mg of "elemental calcium".