A Land Value Tax applies, as the name suggests, only to the value of land, not that of any structures built on it. Most real property taxes apply to both. Thus, the latter somewhat discourage construction for higher density. (Though in practice, zoning laws are a much bigger barrier.)

The intuition behind the LVT is that increases in the value of land, in urban areas, are mostly driven by a growing local economy; therefore the community should benefit from them. Increases in the value of structures, OTOH, mostly come from investments by the property owner.

There's a fascinating book (well, if you have any interest in economics) about the LVT, from 1879, by Henry George: http://www.henrygeorge.org/pcontents.htm