noun
required field; mandatory entry
Used in computing contexts, especially for online forms or database fields that must be filled in.
このフォームでは、名前とメールアドレスが必須入力です。
On this form, name and email address are required fields.
任意入力 means optional input, the opposite of 必須入力.
Compound of 必須 (required) and 入力 (input).