FD3S
Flexible contract is almost certainly a payment per rostered block hour (no basic wage or benefits except staff travel) and no fixed roster pattern. Not quite as bad as it sounds as can make good money if you are flexible and don't mind putting the hours in each month and accepting the lack of life planning ability from month to month. It's comes down to a choice based on personal circumstances. Some hate it, some get on with it and find it's not perfect but it's not too bad after all.
Hope this helps.