Contextually, ''sifu'' is used in a familial manner as a child addressing a parent by the description "father", rather than a self referenced title seen in modern slang usage. It is also commonly used in a martial arts context to denote an instructional relationship.
In mainland China, sifu is a common respectful form to address most professionals where knowledge or skill is exchanged, such as s, , monks, house decorators, and many elders of old trades and arts, with a large amount of experience, such as paintings and calligraphy. It is commonly used to refer to traditional professions where apprenticeship is possible, as this word is the reciprocal of "apprentice" .
It is rarely used and may even be disrespectful when used to refer to people of modern professions such as doctors and lawyers. In addition, it is rarely used to refer to teachers and professors in academic settings.
In modern slang, people use the word so as to, superficially, build up a better guanxi with others, in particular those with whom they are not familiar, not dissimilar from the western terms "boss" and "guv'nor".
Martial arts usage of sifu
Traditionally, in Chinese martial arts, the term was used as a familial term and sign of respect as in the general usage.
The term takes on a more intimate context when a student becomes a formal student or disciple of the teacher. The acceptance as a student is a very formal event, usually requiring a discipleship ceremony called ''bai shi''. After the ceremony, the relationship is defined as a more direct parent/child context and usage takes on this term rather than a generic sign of respect for skill and knowledge.