"(a) kind of ontology in which the world was seen as structured, differentiated and changing. And science was seen as a process in motion attempting to capture ever deeper and more basic strata of a reality at any moment of time unknown to us and perhaps not even empirically manifest. Structures are changing, differentiated" (from the Baskhar interview on raggedclaws.com)
Critical realism takes up what it sees as the epistemic fallacy, that is where the question of ontology 'what is' is reduced to the question of how we know what is. Bhaskar and company want to reassert the fundamental necessity of ontology and show how even those argumenets pitted against it, presuppose an ontology. Truth is thus concieved as making falliable statements about the real.
In political terms critical realism can be seen as an attempt to remove many of the revolutionary and political aspects from Marx's theory to produce a stale academic scientistic idea of objectivity. This is wrapped up in several woolly and often meaningless references to human emancipation; critique of the illusionary, dualistic world and so on. These allusions to a radical project should be taken with a pinch of salt especially since the idea of ontology it markets is one that has little place for politics.