A Limited Time Gift is a Gift that Zynga has released for a certain amount of time (usually 6-8 hours, sometimes 24 hours depending on what it is) so that a farmer can send the gift to their neighbors. Once that time period is up, the item is no longer available for gifting. (decoration)
Some limited time gifts include:
Fuel (small or large can)
for Tuscan Event
There has been many other limited time gifts in FarmVille, but those are some of the main ones.