The blogosphere is made up of all blogs and their interconnections. The term implies that blogs exist together as a connected community (or as a collection of connected communities) or as a social networking service in which everyday authors can publish their opinions. Since the term has been coined, it has been referenced in a number of media and is also used to refer to the Internet.

The term was coined on September 10, 1999 by Brad L. Graham, as a joke. It was re-coined in 2002 by William Quick, and was quickly adopted and propagated by the warblog community. The term resembles the older word logosphere (from Greek logos meaning word, and sphere, interpreted as world), "the world of words", the universe of discourse.

Despite the term's humorous intent, CNN, the BBC, and National Public Radio's programs Morning Edition, Day To Day, and All Things Considered have used it several times to discuss public opinion.

A number of media outlets in recent years have started treating the blogosphere as a gauge of public opinion, and it has been cited in both academic and non-academic work as evidence of rising or falling resistance to globalization, voter fatigue, and many other phenomena, and also in reference to identifying influential bloggers and "familiar strangers" in the blogosphere.