What is the meaning of "Al-Masalih Al-Mursalah" (unrestricted public interests) and "Sadd Al-Dhara'i'" (blocking the means to evil)?

An interest (maslaha) is divided into three categories: The first is the considered interest (al-maslaha al-mu'tabarah), which is that which the Lawgiver has taken into account. The second is the cancelled interest (al-maslaha al-mulghah), which is that which the Lawgiver has invalidated. As for the unrestricted interest (al-maslaha al-mursalah), it is that which the Lawgiver left unrestricted, neither considering nor cancelling it. The ruling on it is referred back to the general principles of Sharia. As for blocking the means (sadd al-dhara'i'), it means prohibiting the means and ways that lead to the unlawful, because the means share the rulings of their ends.