A microblog is a blogging platform where the amount of information that can be shared per author is either enforced to be very short, or just typically very short.
The most common examples of microblogs are Twitter and Tumblr. Twitter limits users’ posts – called “tweets” - to 140 characters. Twitter’s limit is set such that a standard text message, which is limited at 160 characters, can include one entire tweet plus address information. Tumblr has no character limit, but users typically adhere to an “unspoken rule” that shorter is better for posts; many tumblog - the term to describe a public tumblr profile - entries contain only a photo and a brief caption.
The very brief nature of microblogs makes these easy to scale. This means that hundreds of millions of individuals can post billions of status updates per day. According to Twitter, in May of 2011, Twitter was handling 2,200 updates per second, and had 175 million users, but requires far less computational power to maintain than a full-scale blogging website or content management system would require.