An interesting discussion on the nature of a blog: what is a blog? What is this blog? It is not quite a diary as it makes no attempt to be comprehensive i.e. systematically log what happened, when and how. Instead it's highly selective. It's certainly not a private diary as it's published on the internet.
Decide that it's more of a column on a theme - if a definition has to be found.
However it does, of course, have an element of a diary - hence the title.
What makes a good diary? John Bayley, reviewingVirginia Woolf's diary 1936-41 (published in 1984) in the London Review of Books, says hers was a thin and self centred narrative....
"Katherine Mansfield writes in her journal what Virginia Woolf’s Diary continually implies: ‘I must not forget that.’ She must not forget the way the hens looked, and how the rain soaked her thin shoes. A few days before her death Virginia Woolf recorded the haddock and sausage meat. ‘I think it is true that one gains a certain hold on sausage and haddock by writing them down.’"
Good diarists: Pepys (of course), Chateaubriand, Rousseau, Anthony Burgess, Barbara Pym (Bayley's list).
I like primitive diaries: basic logs.