In Colombia and several other places in south america we call that Caucho
A short search for "árbol de caucho" gives us lots of links about "rubber trees" (obviously natural rubber/gum)
Same search give us that in regions like Mexico they call it "Hule". In Colombia this word is understood but not used frequently.
We use goma to refer to the same material but in a very soft or even liquid state. When is solid (but elastic) we call it caucho.
The artificial version of if is called "caucho sintético"
According to several sites including this http://wikidiff.com/gum/rubber the difference is this
- gum = any of various viscous or sticky substances that are exuded by
- rubber = pliable material derived from the sap of the
rubber tree; a hydrocarbon polymer of isoprene
So gum is the sap of the tree in liquid state and that is what we call "goma" while rubber is the already processed material and that is what we call "caucho" or "hule" depending on the region.