Micro blogging is the minor version of blogging that allow you user to write entire up to 140 character. Its refer to the posting is very short update about onself.It is an contrast to long-form blugging.
Usually status in your Social Network site like Facebook can also be considered as Micro Blogging. The same thing can be said for Foursquare.
Microblogging is a broadcast medium in the form of blogging. A microblog differs from a traditional blog in that its content is typically smaller in both actual and aggregate file size. Microblogs "allow users to exchange small elements of content such as short sentences, individual images, or video links".