When I've heard the specifc term "Mortgage Freedom Account" it was referring to a side account earmarked for mortgage payoff. The idea was instead of prepaying the mortgage any excess "principal" payments were directed to the side account. If nothing unexpected happened, the side account would eventually meet or exceed the mortgage balance and you could decide to payoff the morgage in full at that time (or not, as you wish). Until then, if the unexpected happened, house prices tanked, prolonged unemployment, financial emergency at a time when HELOC was unavailable, etc, you could tap the MFA for whatever money you needed under circumstances where you might not be able to tap home equity (if you had been paying into the mortgage). It was also supposed to help allow the option to walk away from an upside down (non-recourse) mortgage if a small downpaymet deal went bad in a housing crash.
Because everyone seems to love Freedom in the name, it seems like the term is now being used for all type of plans (and schemes) which are mortgage related. You have to get more info about what someone means when they use this term now.