Blog is a shortened name or common name for weblogs. These were originally updates from software developed and various important people about things they were working on, developments etc. They were particularly common in the early days of online gaming, multiplayer games, etc.
With the advent of programs such as Wordpress, blogs have come to the masses, now we know when everyone and their dog takes a dump or passes gas.
Examples of porn blogs:
* Pornpig's Porn Party - Updated from a number of sources daily * DDcup Big Booby Blog - Specifically geared towards lovers of big tits.