A notary of any kind is someone authorized to perform specific legal formalities, including drawing up or certifying contracts, mortgage documents, deeds, and more.
All notaries, no matter how they perform their service, must watch as someone signs a document. Historically, this has required that the notary or signer must travel to meet one another in person where the notary serves as a witness during the signing event.
The online (remote or digital) notaries are the same as the traditional notaries, but they perform the notarizations over the internet via digital tools.