The teacher or doctor or parent should probably specified further, either by the definite article or by some adjective. You also need to know whether you are referring to one teacher or more than one. There are many ways to do it: Correct ways to speak about one particular teacher: I don't understand my teacher's jargon. I don't understand the teacher's jargon. I don't understand that teacher's jargon. I don't understand this teacher's jargon. Correct ways to speak about a group of teachers that you know: I don't understand the teachers' jargon. (in English, unlike Portuguese, there is no distinct plural form for the definite article "the") I don't understand these teachers' jargon. (notice how "these" agrees with "teachers" in number: both are plural) A correct form that presents some difficulty: I don't understand teacher's jargon. With no article or adjective, this expresses the abstract claim that I never understand teachers when they use their own technical language ("teacher's jargon"). In that case, "teacher" is the category of persons who are teachers, and does not refer to any one teacher. I think it could also be written "teachers' jargon" referring to all teachers everywhere. In more informal settings, you could say "teacher speak" or "teacher talk" to communicate the same thing as "teacher's jargon." Sometimes it is even hyphenated: "teacher-speak."