FIDIC Red Book: Difference between lump sum contract and Fixed sum contract

My understanding is that it is a lump sum contract under FIDIC red book, although the payment under the contract sum is proposed by using the bill of quantities, with fixed item rates, but for the actual quantities of work measured under those bill items, executed as per the scope of work defined through the contract drawings and specifications.

Is my understanding correct?

A Fixed Sum, Fixed Price, Lump Sum or GMP contract are, in effect, all different names for the same thing. That is, they refer to contracts which are NOT re-measurable and not subject to some form of incentivisation.

FIDIC Red is something of a hybrid as it is generally a fixed price BUT with a variation being triggered if quantities change substantially (10%).