isreg nickname v1 is a normal nick on channel v2

what does this mean ?

that nick is not op or hop or ... ?

Yeah, it's just a normal user.

Not Opped, Not voiced, Not Half-Opped, Not an IRCop, just average Joe

The isreg operator does not define between a user and an IRC Operator, it's based upon status inside the channel.

Expanded, it means 'is regular'.

Regards,