Undergraduate research experiences have the potential to motivate undergraduate students to pursue a career or go to graduate school in science and engineering and also contribute to students’ technical and professional skills. Although STEM faculty and education scholars agree that research experience is important for undergraduates, there seems to be a lack of a concrete definition of what the word “experience” means. Based on interviews of undergraduates, graduate students, and PIs in two engineering laboratory groups, we noticed that they all used the word “experience” often and with a variety of implied meanings. Through qualitative coding of the interview data, we identify four categories of how interviewees talk about experience. The categories are 1) practical experience: “real-world” opportunities that simulate research done in industry or graduate school, 2) social experience: the interpersonal, communication-based aspects of working in a lab, such as interactions between lab members, 3) professional experience: learning skills that are applicable to other aspects of students’ lives beyond the specific research environment, such as how to manage time, 4) epistemic experience: learning and applying abstract engineering knowledge, theories, and concepts. By deriving a typology of kinds of “experience,” we can reduce the ambiguity that exists in scholars’ notions of experience in education as well as in the implicit expectations of undergraduates and their research mentors, which can create strategies to increase the retention and persistence of students in STEM, and promote STEM disciplinary knowledge and practices, integrating students into STEM culture.