op = @
voice = +
half = %
??? = a

*chanserv sets mode +a somenick

a = admin ?

a is channel admin on some servers, i've seen it use these prefixes: &, ! and *

thanks! thought it was admin but wasnt sure

! is +u (which is founder on the servers i've seen) but theres different mode prefixs so it's really anything

This all depends on the IRC software or "IRCd" Most common that i know of... is..
Confernce Room Which has the following modes (www.webmaster.com)
@ - Op +o
+ - Voice +v
- - The Thing under Op :tongue: +u

Unreal IRCd - Which The network i am uses. (unrealircd.com)
We have the following enabled.. ...
~ - Owner/Founder of Chan +q
& - Sop "Admin" of chan +a
@ - AOP "Op" of chan +o
% - HOP "halfop" of chan +h
+ - VOP "voice" of chan +v

UltimateIRCd - Is the following
(aohv)!@%+
! - Admin/Founder +a
@ - Op - +o
% - Halfop - +h
+ - Voice +v

Here is EFNet runing Xylon? IRCd... probably custom
(ov)@+
O - Op @
V Voice +

Basicly you pretty much get it! i hope my pointless guide to your already answered question is helpful

nice guide gamersad.