One day I was typing an e-mail to my friend on my iPhone and was having a blah kinda day. So, in the subject line for the e-mail, I typed "Blah". Or so I thought. Autocorrect changed it to "Borg". Since then, it has remained a subject header we use when we have no subject.
I will NOT steal from Jerry Seinfeld and suggest that this is a blog about nothing. However, you may draw your own conclusions.
Either way, welcome aboard.