Confused about search tabs ?
 

What is the meaning of the "maximum number of simultaneous searches" choice in the options menu?

When I perform a search, do I have to wait for the spinning lime to stop before I start another search? or does this mean I can enter search after search until I reach the limit?

How do I know if I've passed the limit (without looking at the options menu)?

The number of searches is how many you can have open at one time. Once you go past the limit, your oldest ones start to disappear.