A taxman is someone who works for the government and collects taxes from people. He's often seen as a bit of a necessary evil.
When we talk about the taxman, it usually means that person who comes to your house or business to collect money that you owe in taxes. It can be kind of intimidating, but remember, he's just doing his job! In some cases, when people say "taxman," they might also be referring to a computer program or system that calculates and collects taxes automatically. This is less common, but still happens sometimes.
(sometimes derogatory) A tax collector.
