Blockchains are add-only distributed peer-to-peer ledger databases which stores normally coin transactions.
With the creation of „Smart Contracts“ we have the possibility to write in the blockchain a program which takes, processes and returns other kind of data (theoretically any, practically there are currently some limitations with respect to mature programming languages, e.g. PHP or Java).
Semweb has interfaced a private ethereumj instance network with its major system – SKOS Shuttle – where sub graphs are stored / retrieved to / from the blockchain. Read more details on this on SKOS Shuttle Blockchain Tutorial.
Securing Thesauri in blockchain prevents from uncontrolled changes to them, guaranteeing secureness of content.