Section 43 of IPC : Section 43: "Illegal" or "Legally bound to do"

Explanation using Example

Example 1:

Ravi is a shop owner who sells fireworks. During Diwali, the government issues a ban on the sale of certain high-decibel fireworks due to environmental concerns. Despite the ban, Ravi continues to sell these prohibited fireworks. Here, Ravi's action of selling the banned fireworks is "illegal" because it is prohibited by law. If caught, Ravi can be prosecuted for violating the ban.

Example 2:

Sita is a witness in a criminal case involving a robbery. She receives a court summons to testify about what she saw. Sita decides not to appear in court despite the summons. In this scenario, Sita is "legally bound to do" her duty of appearing in court and testifying. Her failure to do so is illegal because she is omitting a legal obligation imposed by the court. Sita can be held in contempt of court for not fulfilling her legal duty.