师父(shī fu) - master, teacher in Mandarin

师父 (shī fu) is a master in the traditional apprenticeship sense: the person who takes you on and teaches you a craft, a martial art or a religious practice, and to whom you owe lasting loyalty. It is also the ordinary way to address a Buddhist monk or nun.

Now the trap, and it is a real one. 师傅 is pronounced identically, shī fu, but is a different word. 师傅 is how you politely address a skilled workman you do not know: a taxi driver, a plumber, a chef, a security guard. 师父 with 父 (father) is your own master, a personal relationship. Calling a stranger 师父 sounds oddly intimate; calling your kung fu master 师傅 sounds like you have mistaken him for the bloke who fixed the boiler.

Note the neutral tone on the second syllable in both. And keep 师父 apart from 老师 (lǎo shī), which is a schoolteacher or a university lecturer, the ordinary institutional word.