In contrast with ramblings, which carry a slightly more negative connotation, musings are a string of thoughts characterized more by their contemplative nature than by their strung-together quality. They are everywhere in the blogosphere because they are valuable yet egalitarian commodities; they can be priceless, but everyone can have a piece of them.
They are meditations or reflections on any subject, from the sociopolitical and the confessional, to the sacred and the profane. They can be a conscious decision to let your stream of thoughts flow, or inadvertent mental wanderings that transport you to the most unexpected places.
Musings have been around as long as the mind has, but they were made particularly popular through the stream of consciousness mode in modernist literature, by writers such as James Joyce, Virginia Woolf and William Faulkner. Yet this flowing form of expression is far from frozen in the past; it has survived modernism and reflected, contemplated and meditated itself into postmodern literature, surfacing in the writings of Bret Easton Ellis and Jonathan Safran Foer, among others. Rest assured, people will continue to muse for years to come.