Broad-spectrum refers to a cannabinoid extract that contains a wide spread of legal cannabinoids. A broad-spectrum extract will contain, other cannabinoids, waxes, lipids, fats, residual plant matter and oils, flavonoids and terpenoids.
For a broad spectrum to be legal, it needs to be THC free.
Therefore a true legal broad-spectrum extract is very rare as there are many cannabinoids that are illegal in the UK.
CBD isolate is a further refined extract. It only contains CBD and no other cannabinoids. Isolate is only one of the Cannabinoids in its purest form, however, there are benefits from all the elements found within the broad spectrum extract and they work in conjunction to provide a more rounded result.