“Literally, land speculation would be the act of buying land to sell it for more in the future, ceteris paribus. This kind of speculation is very rare because of the cost of transferring ownership.”
“It is therefore preferable to define land speculation as the act of a landowner who refuses to sell his land, even at a price higher than its use value, in the hope of a future increase in prices.”
Source: http://www.fao.org/docrep/005/x2038f/x2038f09.htm#TopOfPage
Some articles from CITEGO to go further: http://www.citego.org/bdf_descripteur-1116_en.html