Very simply, “microblog” is the generic term for what Twitter is. Tumblr blogs (“tumblelogs”) are also technically microblogs. The Wikipedia article on Microblogging is pretty good for more on this, and Manton Reece is one of the most prominent voices in the space if you’re interested in more!
I’m also on Twitter (@johnholdun) but I’ve decided not to keep these in sync, mostly because this non-Twitter microblog is extremely mundane the mundanity now lives at @johnholdun2, powered by this script I wrote.
This microblog is powered by a homemade set of PHP scripts that turn index.md files into index.html files; all my updates are written from a web interface that just creates a timestamped Markdown file with whatever I write in a textbox. The system is too disparate to actually release, but if you’re interested in some code samples you should email me.