unlimited use; all-you-can-use
Often used in service plans, subscriptions, or promotions where a fixed fee allows unrestricted usage.
This app is available for unlimited use at 500 yen per month.
If you sign up for the unlimited plan, data usage becomes unrestricted.
無制限 is a more formal term meaning 'unlimited' or 'without restrictions', while 使い放題 is a common compound used in commercial contexts.
Compound of 使い (stem of 使う 'to use') + 放題 (suffix meaning 'as much as one likes').