Mini Perm

Short-term financing used to pay off income-producing construction or commercial properties, usually payable in three to five years.

In this case, "perm" is short for "permanent", alluding to permanent financing. Mini perm financing is something a developer would use until a project has been completed and can therefore start producing income. In other words, a developer will use this type of financing prior to being able to access long-term financing or permanent financing solutions.