This chapter explores the concepts of radicalization, extremism, violent extremism, and terrorism, unpacking their descriptive definitions, diverse interpretations and offering implications for social work practice in countering violent extremism (CVE) contexts. The discussion begins by exploring the conceptual evolution of radicalization and models of radicalization. Notable critiques of certain radicalization models are provided, underscoring the importance of more current multisystemic frameworks and dimensional models that include mixed or more hybridized forms of violent extremism, and risk factors of radicalization in recent years. While these concepts are embedded in terrorism and extremism studies and social work practice, the meanings and application of these concepts are numerous, influenced by organizational mandates, cultural contexts, and disciplinary priorities. This chapter summarizes the practical and theoretical implications of these conceptualizations for social workers, questioning the way these terms may impact social work’s approach to CVE, and proposes that the profession ought to navigate the ethical and practical challenges posed by these terminologies to develop more effective, context-sensitive interventions.