mandatory

adj

1. obligatory; required or commanded by authority.

   “Attendance at a school is usually mandatory for children.”

   “This kind of immediate control structure we take to be characteristic of the tribe, and it leads to a rather rigid type of system in which 'every action not mandatory is forbidden'.”

   “It also discusses the access to legal instruments for enforcement with regard to mandatory disclosure of environmental information.”

   “While in the most serious cases mounting an investigation is usually mandatory, there are other occasions where it is less clear-cut or when it is concluded that an investigation would not fulfil RAIB's objectives to improve safety or prevent future accidents.”

2. Of, being or relating to a mandate.

   “Mandatory Palestine”

noun

1. A sign or line that require the path of the disc to be above, below or to one side of it.
2. (dated, rare)A person, organisation or state who receives a mandate; a mandatary.