What is altcoin exchange?

Could you elaborate on the concept of altcoin exchange? I'm curious to understand how it differs from traditional cryptocurrency exchanges. Specifically, what types of altcoins are typically traded on these platforms? Are there any unique features or services that altcoin exchanges offer that set them apart from their counterparts? Additionally, what are the risks involved in trading altcoins, and how do altcoin exchanges mitigate these risks? Your insights would be greatly appreciated.