Online diaries have existed since at least 1994. As a community formed, these publications came to be almost exclusively known as online journals. Today they are almost exclusively called blogs, though some differentiate by calling them personal blogs. The running updates of online diarists combined with links inspired the term 'weblog' which was eventually contracted to form the word 'blog'.
Later private and secure online diaries popped up. These replace the book you had under your bed pillow and allow users to store their inner secrets securely online.