A cavity wall is two skins of masonry to form a structure.
Usually blockwork would be used as an internal skin,
which would be plastered on the inside,
for the external skin as a decerative feature.
The picture below shows a cross section image of a cavity wall,
made of brickwork and blockwork.
Including correctly installed insullation and wall ties.
Repointing Brickwork - Isle of Wight
Islandwide Service