Blockchain is the technology behind Bitcoin.
Onyx uses it to send documents to the Bitcoin Blockchain to prove a doc was recorded at a certain time.
We do the eCertify for the 2nd largest Recorder in the US - Cook County Illinois https://www.ccrecorder.org
To read and learn more about blockchain, here is the Wikipedia link Blockchain
Why do we record docs to the blockchain? Bitcoinist has a good explanation.