Do you not have access to a search engine? I got a dozen articles on it from a quick search.
It is (or perhaps was, it is still around but today goes under the name UKIE/The Association for UK Interactive Entertainment) mostly a UK trade group (it started out aiming to be European but never quite stuck the landing so retreated to the UK) doing all the sorts of things trade groups do (voice in government, lobbying for tax breaks, trying to ensure integrity of product aka anti counterfeiting and anti piracy efforts, some promotion around the world, at one point tracking sales data...) for "entertainment software publishers"* and much like trade groups elsewhere** it also had a hand in ratings for games within the UK (while the traditional BBFC system with the circles with a number in it was a thing for some games it was not required save for higher end violence and sex) before it was phased out in favour of the PEGI system that most of Europe uses.
*the devs themselves, despite the efforts of ELSPA/UKIE to merge, do have The Independent Games Developers Association aka TIGA.
**see various German efforts, the comics code authority in the US, and the Hays code in the US for films, and RIAA "this may have explicit lyrics" thing for music in the US. Such things are deemed a popular alternative to having governments do it, though I have my misgivings with such things.