It's possible to change or add ticket states. There are two important options, state-name and state-type.
The default state-types are 'new', 'open', 'closed', 'pending reminder', 'pending auto' and 'removed'.
Each state needs to have a name (state-name) and a type (state-type). The name is free settable.
Use the Admin-Interface (Status defs) if you want to change or add ticket states.

Take care that you also update some config options if you changed/rename the state "new". Add to you Kernel/Config.pm:
[...]
# PostmasterDefaultState
# (The default state of new tickets.) [default: new]
$Self->{PostmasterDefaultState} = 'new';
[...] |
Take care that you also update some config options if you changed/rename the state "open". Add to you Kernel/Config.pm:
[...]
# default phone new state
$Self->{PhoneDefaultNewNextState} = 'open';
# PostmasterFollowUpState
# (The state if a ticket got a follow up.) [default: open]
$Self->{PostmasterFollowUpState} = 'open';
[...] |