It's probably quite apt that definitions of post-rock, and even the credit for who/when the phrase was first coined and attributed, are amorphous. Although mentions of "post-rock" can be found leaving a breadcrumb trail through music press reviews since as early as the 1970s, it seems broadly agreed that the description of the genre as it has been (generally, loosely, by no means comprehensively) understood since the mid-to-late 90s was that of music writer Simon Reynolds.

Reynolds first used the term in Melody Maker as well as in a Mojo magazine review of Bark Psychosis' Hex in 1994, but the much cited description that he used is in an feature from The Wire a couple of months later, in which he discusses music that uses "rock instrumentation for non-rock purposes, using guitars as facilitators of timbre and textures rather than riffs and power chords."

It's a neat summary of a sound that remains difficult to pin down, or rather, a collection of astringent, emotive, sometimes abrasive, sometimes awe-inspiringly beauteous sounds made by a set of bands that often seem to have little in common with each other besides the label.

So what are its origins? With this year's twentieth anniversary box set reissue extravaganza, there's been much mention of Slint, particularly their masterwork (and second of just two albums) Spiderland, as being, if not one of post-rock's earliest practitioners, then certainly a band and a release that were to foreshadow it and influence its later proponents. Also hugely influential, although significantly different in style, were Talk Talk, who evolved radically from their early synthpop/new wave sound in the early 1980s through to the jumble of rock, jazz, ambient and classical stylings of Spirit of Eden in 1988.

The 1990s was the decade when post-rock really flourished. Stereolab's take on the genre was strongly indebted to '70s krautrock with which post-rock undeniably shares elements (the repetition, the lack of obvious "rock and roll"-type song structures, the frequent lack of vocals), which they combined with the louche, lounge-y feel of '60s pop music. Bark Psychosis, meanwhile, saw the use of the loud-quiet-loud dynamic range that, too, has remained one of post-rock's most common identifiers.

Another key band were Tortoise, whose sound played with with jazz, minimalism, dub and more. Their 1996 release Millions Now Living Will Never Die (even the title of which is, somehow, archetypal post-rock-speak, or represents what has since become so) was to influence many musicians. Interestingly, one David Pajo, formerly of Slint, joined the band at this time.

From their Montreal base, a wave of significant post-rock bands emerged via the Constellation Records label, including perhaps most prominently Godspeed You! Black Emperor (originally active from 94 to 2003, and then resuscitated again in 2010), along with associated acts like Thee Silver Mt Zion, featuring Godspeed's Efrim Menuck, as well as Toronto's Do Make Say Think.

Probably one of the bands most strongly associated with the genre are Glasgow's Mogwai, who have been spinning their shimmering, bludgeoning, alternately enervating and calming and ever-evolving sounds since 1995. In recent times the ethereal Icelanders Sigur Rós have been popular partly thanks to the uptake of their music for soundtracks, Texans Explosions in the Sky's "cathartic mini-symphonies" have enraptured live audiences (including those at the All Tomorrow's Parties festival that they curated in 2008), and Sheffield's 65daysofstatic have, simply, scorched the ears and raised goosepimples on the flesh of anyone lucky enough to have witnessed their incredible gigs. In March this year they played a London show to mark the 10th anniversary of their first album The Fall of Math, performing it in its entirety.

Perhaps it is thanks to post-rock's lack of clear defining characteristics, or strong visual identity, that the genre has managed to outlive other, more ephemeral styles. Never hugely in fashion, it had less chance, perhaps, of falling out of fashion. Of course, it also helps that many of its practitioners are the kind of cerebral, proficient and almost by definition experimental musicians that are least likely to rest on their laurels and more likely than most to force the evolution of their own bands' sounds, and by extension that of the whole genre.

So just this year, as well as the retrospective remasters, the box set and associated documentary to mark Spiderland's anniversary, we have also already seen new releases by both Thee Silver Mt Zion, whose Fuck Off Get Free We Pour Light on Everything is every bit as dramatic, vigorous and inspiring as anything from the last twenty years (if you get a chance, listen to the 11-minute 'What We Loved Was Not Enough': it's stunning). Mogwai, meanwhile, have given us the subtle electronica of Rave Tapes, following hot on the heels of their graceful soundtrack for last year's haunting French psychological/zombie drama Les Revenants. Post-post-rock? Nah. Not while the genre itself is still as vital and vibrant, as dynamic and as inspiring as it looks set to continue being, for a while longer yet.