Blank nodes are part of the RDF specification. They are "nameless" nodes in the RDF graph.
Much has been said about them (On Blank Nodes (2011), Blak nodes considered harmfull (2011)). They probably were a mistake.
The also break the ability to efficiently reason over data (Simple and Efficient Minimal RDFS (2009)).
The openEngiadina project follow previous suggestions not to use Blank nodes when publishing content (How to Publish Linked Data on the Web? (2007)).
The process of replacing blank nodes with newly minted IRIs. The process is named after the mathematician Thoralf Skolem (see why).
The W3C has a wiki entry on Skolemization.