A calling or vocation that requires specialized knowledge and lengthy, intense preparation is referred to as a:

A calling or vocation that demands specialized knowledge and extensive training is best described as a profession. Professions typically require a significant commitment to education and skill development in a specific field. This can include formal education, practical training, and often the acquisition of certifications or licenses to practice within that field. Professions are characterized by a high degree of expertise and typically demand adherence to established ethical standards.

In contrast, a job generally refers to any work that one may do for payment, without the requirement for the extensive education and training that a profession necessitates. Public service involves working for government or community-oriented roles, which may not always have the same level of specialized knowledge required as a profession. Personal achievement refers to an individual's accomplishments, which can occur in a variety of contexts and do not inherently relate to the demanding nature of a profession. Thus, the term 'profession' is the most accurate descriptor for a vocation involving specialized knowledge and intensive preparation.