Sifu - (師父) - a Teacher, or a Master of the art. Also a father figure.
It used to imply more of a master of the system, but now a days it just means "teacher" more than anything as many Sifus have not masterd the art.
Use capital "Sifu" for your Teacher. a.k.a SiFu or Si Fu
In the West it is generally used before a teacher's last name. i.e. Sifu Smith. In the East it is commonly used after a sifu's last name. i.e. Chong Sifu. However in many cases you will see it used before a fist name, i.e. Sifu Eddie.