Reviewthe "the world of ($foo)" was the decca group's budget-price label, starting sometime mid-late sixties or early seventies, and eventually effectively replacing their "ace of clubs" label, which had been positioned as a mid-price range - though this may've lasted until the decca eclipse label was launched, and a success.
the "world of" might be that of an artist or group; a band or a band-leader; an orchestral conductor or an ongoing radio show; a year or a decade; a pop music or dance craze or style, or a traditional form; a classical or light composer or - well, yr hmbl srppnt. isn't actually aware of a "the world of steam locomotives" - but there could have been. . .
it was where aught decca'd given up on trying to sell on lps at full price or even mid-price could end up, and sell through rackers' shelving units in non-traditional outlets as well as through record and music shops and departments. much - most? - of its catalogue was reissues of albums previously released at full price, but there were also original compilations, and fix-ups of material previously released on the dead or dying ep format, as well as some decca sound-alike chart-covers albums.