Unlimited Bonus is referring to a bonus that is being given on a permanent basis and it will not stop.
On the other hand, if there is a website that is providing you with free 25 spins then that is a temporary bonus also known as a welcome bonus. This is not considered an unlimited bonus because once the spins are over your bonus has expired.
Unlimited bonuses never expire. These are the types of bonuses we look for in this site. These are the types of bonuses you are probably looking for yourself likewise.