Semantic Wikis try to combine the strengths of Semantic Web (machine processable, data integration, complex queries) and Wiki (easy to use and contribute, strongly interconnected, collaborativeness) technologies.
Goals are diverse and include:
simple annotations of existing Wiki content;
tools that guide users from informal knowledge contained in texts to more formal structures;
full-fledged tools for ontology editing where the text is no longer in the focus of the system.
In the future, Semantic Wiki systems might play an important role for "knowledge acquisition", enabling non-technical users to contribute to the Semantic Web.