Crémeux
Crémeux — French for "creamy" — is a dense cream layer that sits between a ganache and a custard. Most often it is an anglaise into which chocolate, fruit purée or gelatine is introduced, after which the mass sets as it chills.
What separates it from a mousse is the absence of aeration: it is not whipped, so it stays dense and smooth. What separates it from a ganache is the yolk and dairy base, which gives a softer, less fatty texture.
In modern entremets crémeux is used as an insert — an internal layer that creates textural contrast and concentrates flavour. It is frozen in a ring or silicone mould, then set inside the mousse during assembly.