Given that the term ‘plagiarism’ is open to multiple interpretations, resulting in confusion among students and teachers alike, research that investigates the current state of empirical evidence and sheds light on students’ ability to define and detect this notion has important pedagogical implications. This study examines undergraduate English Language Teaching (ELT) students’ understanding of plagiarism in academic writing through qualitative data collection methods. After the focus group filled in the open-ended questionnaire, they were exposed to two sets of texts each containing an original, a plagiarized and non-plagiarized copy. The copy in the first set featured mainly word-for-word plagiarism while the copy in the second set was plagiarized in terms of illicit paraphrasing. The students were asked to identify whether there is any plagiarism in each copy and assess the texts regarding their acceptability in the format of an interview and think-aloud protocols. The results of the open-ended questionnaire and interviews were compared revealing that although all the students were able to define plagiarism correctly, most of them failed to identify it in the written text. The study also uncovered discrepancies in how the students view the aforementioned types of plagiarism.