A pardon is when someone forgives or excuses an action that was wrong. It's like saying "it's okay" after something happened.
Imagine you accidentally broke your friend's favorite vase. They could get angry and scold you, but instead they say "oh well, it's just a thing, don't worry about it." That's a kind of pardon. In a way, you're being forgiven for breaking the vase even though it was still wrong to do so.
In other words, when someone says "pardon me" or asks for your pardon, they usually mean that they want to be excused from something. Like if you spill food on their new shirt and they say "oh no, pardon me", they're asking not to have to deal with the mess.
Forgiveness for an offence.
To forgive (a person).
Often used when someone does not understand what another person says.
