A consecutive-day pass provides unlimited rail travel for the duration of the pass, once it has been validated. For example, if you buy a one-month pass you can travel on as many trains as you like on any day during that month.
A flexipass gives the pass-holder a two-month period during which to use the number of days specified by pass. For example, if you buy a two-month flexipass with 10 days of travel, you can use each of those ten days at any point during the 60-day validity period.