What term refers to a person who has assumed day-to-day care, custody, and control of a minor for a substantial period of time?

The term that accurately describes a person who has taken on the day-to-day care, custody, and control of a minor for a significant period is "De Facto Parent." This designation applies to individuals who may not have a legal relationship defined by adoption or guardianship but serve in a parental role and have established a sustained and significant emotional and physical bond with the child.

In legal contexts, a de facto parent may qualify for certain rights or responsibilities regarding the child based on the length and nature of their caretaking. This term is important in family law cases, especially when determining custody arrangements or the legal recognition of an individual's contribution to the child's upbringing.

In contrast, other choices refer to different roles that do not fit the definition provided in the question. A dependent indicates a person under the care of another but does not imply the caretaker relationship described. A guardian ad litem represents the legal interests of a child in court but does not necessarily provide ongoing care. An adoptive parent has gone through a legal process to become the child's parent but may not have fulfilled the condition of extensive prior care. Therefore, "De Facto Parent" correctly captures the essence of someone acting in a parental capacity without formal legal status.