Is someone able to tell me the difference between pro rata...

Is someone able to tell me the difference between pro rata shortfall and underwriter's short fall?

Also what does "best endeavours" basis mean?

They are terminologies that were used in the announcement last night. I'm very tempted to pick up a couple of million BRTO's if they are available. I'm prepared to sit and wait until BRT hits 20c+ in the next 5 years. I believe there is fairly minimal risk in buying BRTO's