Forums mIRC Help What does & mean?

I know there is ~, @, %, and +, but what is &? what does it mean? what does it do exactly?

The usage of ~ and & are specific to the network, and not supported on all networks. In regards to the networks that I have seen them used on, here's a little chart that you can use.
~ Founder
& SuperOP/Channel Admin
@ Channel Op
% Channel Half-Op/Help-Op
+ Voiced

That is in the normal order, from highest to lowest.

As to what it does, it just allows an additional level of control in the channel, higher than ops, but lower than founder.

! is also used for Admin. & is also referred to as a Protected Op and if you happen to have all of those modes, the order would be:

~, !, &, @, %, +, N/A

And, as RusselB mentioned, this is specific to each network (some only have @ and +). And what the different modes let you do on a given network can vary, so it's best to check with that network's #help channel for details (or just try it out).