What type of election is held when a Member of Parliament dies or resigns?

Okay, so when a Member of Parliament, or MP, leaves their position unexpectedly – maybe they've passed away, resigned, or taken on a role that disqualifies them – we need a way to fill that vacant seat in the House of Commons. That's where a by-election comes in. Think of it as a mini-election held only in that specific constituency to choose a new MP. It's different from a general election, which happens every few years and involves the entire country voting for all MPs. The term "by-election" literally means an election held "by" the way, or in between scheduled general elections. It ensures that every area of the UK is always represented in Parliament. The other options just don't fit: a coalition refers to when two or more political parties join together to form a government, pre-selection is the process parties use to choose their candidates, and random selection isn't used to choose MPs!