I'm a bit hesitant to post this question here because it regards definitions that are likely trivial, and please note that I'm cross-posting this question from Math.Stackexchange (posted nine days ago, one upvote, no comments or answers): http://math.stackexchange.com/questions/406247/understanding-the-definitions-of-lattice-packing-invariants

I hope this is appropriate.

I'm looking for definitions regarding the meaning of a few lattice packing constants, and internet searches haven't helped very much. Specifically, I'd like to know formal definitions for the two- and three-dimensional lattice packing constants: "thickness", "volume", and "center density" (definitions that appear, for example, with a WolframAlpha search for "A5 Lattice" http://www.wolframalpha.com/input/?i=A5+lattice). I would guess here that "volume" refers to the volume of the lattice unit cell.