Former means something or someone from an earlier time that is no longer in that position or state. When you talk about a former teacher, you mean someone who used to teach but doesn't anymore. A former champion held the title in the past but has since lost it or retired.

The word helps us talk about the past without confusion. If you say “my teacher,” people assume you mean your current teacher. But if you say “my former teacher,” everyone knows you're talking about someone who taught you before. A former president is someone who once led the country but whose term has ended.

You'll also see former paired with latter when comparing two things. If someone says “I like both soccer and basketball, but I prefer the former,” they mean soccer, the first one mentioned. The latter would be basketball, the second one. This pairing gives you an elegant way to refer back to things without repeating yourself: “Between studying hard and cramming at the last minute, the former approach works much better.”