Scarcity is the total supply of an ASSET. In other words, how many copies of an ASSET are available for game designers, gamers or collectors to purchase from The Sandbox's marketplace.
Scarcity is defined by the CATALYST that you add to your ASSET.
There are four different CATALYST tiers, all of which define the maximum possible total number of copies of an ASSET.
Up to 25
Up to 20,000
Up to 50
Up to 4,000
Up to 75
Up to 1,500
Up to 100
Up to 200
In other words, the higher the tier of the CATALYST is, the more scarce (or less common) an ASSET is.
ASSETs which are of very high quality (for example, being designed well, having great small details and have well-made animations) which are also unique will likely be in good demand by game designers, gamers and collectors. The stats that an ASSET has through the use of GEMs is also a factor in its value.
High quality ASSETs which are scarce (have fewer copies) will also probably have a higher value than more common ASSETs. For example, someone who really likes frogs will possibly want to collect high-quality frog-related ASSETs and may be willing to pay a premium price for them if they are rarer.