Deregulation is the name for that change — the policy, or the stretch of years, when a government removes or loosens rules on a kind of business. You will hear 'airline deregulation' or 'financial deregulation': not one afternoon's decision so much as a direction. Papers and politicians use it; ordinary chat usually says 'they took the rules away' instead. Like the verb, the noun is not automatically good or bad. Some people tell it as a freedom story; some tell it as the background to a crash. Though actually, a country can loosen rules in one field and keep tight rules in another, so the word is safer when it says which business it means. In that wide meaning we usually say deregulation, not 'a deregulation', unless we mean one specific round of it.