In release strategy PR

in characteristics we have status in basic data

if i select by F4, then possible outcomes comes,

1. In preparation

2. Locked

3. Release.

what does it mean these 3.

correct me if i m wrong,

if i m using this characteristic to 3.Release my PR in ME54n, it will allow me to release.

if i select Locked than i think if will not allow me to make PR to release.

than what is In preparation mean here

plz help me out