Slots can in an easy way be described as the total amount of "free spots" to receive new conversations. Every agent has a set amount of slots, the same amount as Max Active Chats.

An example: Matilda has four slots available. At the moment she has one active chat conversation. She therefor has one slot taken, and three slots available and free.

If there are several agents online, your Conversation Dashboard will show you the total amount of free slots for these agents. And of course how many of these that are "taken". This helps you to make sure there are always available slots and agents to receive your visitors conversations.