Is a paste made from sugar & glucose and is used to cover cakes. It comes in white usually and you can use food colours in it.
Simple so far, but - different manufacturers give it different names and it's known by different names in other countries.
Americans (and posh people) tend to call it 'Fondant'.
You'll see people telling you to only use this paste or that paste - it's personal preference to a point.
The supermarkets' own brands tend to use the cheaper Xanthan gum (E415), which I find gives a slippery, wet texture to the paste.
The better brands use the more expensive GumTrag (E413) which gives a firmer and easier to work with texture to the paste.
Some, like Covapaste use a mixture of both gums.
Like I say, it's a matter of personal preference but I don't like using pastes which contain only Xanthan gum.