Once a bill has been formally approved by the executive -LRB- in presidential systems -RRB- or the formal head of government -LRB- in parliamentary systems -RRB- and consequently become law -LRB- `` adopted '' -RRB- , it is called an `` act '' , but the two terms are often used interchangeably in popular usage -LRB- or some moments of scholarly imprecision -RRB- .

Once a bill has become law , it is thereafter an act ; but in popular usage the two terms are often treated as if they meant the same .
