This is a term used to describe a method of construction that encapsulates the electronic components in resin during manufacture; this resin then solidifies to form a solid in-assessable plastic block with just the gold connections visible.
This provides a barrier from dust and moisture and protects the delicate electronics but also provide a more robust device to make the casing thinner and therefore cheaper to manufacture.
The usual techniques used for recovery become severely reduced with very few cheap recovery options available.