Science, technology, engineering, and mathematics (STEM) is widely visible in education and workforce policies and discussions in the United States (US). However, there is a lack of consensus on what is considered a STEM career. In addition, little is known about how K-12 teachers conceptualize STEM careers and how this information is portrayed to students. This mixed methods study investigated 52 K-12 teachers' conceptions of STEM careers and if they included this information in their classroom instruction. The data collected consisted of a questionnaire and follow-up interviews with a subset of teachers. The data analysis revealed that there was a range of how teachers defined and conceptualized STEM careers from narrow to very broad. This led to the development of the STEM-Peripheral, Adjacent, Central (STEM-PAC) career classifications which categorizes careers based on the application of STEM knowledge and skills. Additionally, teachers articulated benefits and drawbacks of including STEM career information in their instruction. Benefits included increasing student interest in STEM careers and making learning relevant. Drawbacks included limits to teacher time and knowledge. This study suggests teachers should present STEM as it is connected to various careers and that administrators should support teachers who wish to include this in their curriculum.