Effective assistance of counsel refers to the constitutional right that guarantees defendants in criminal cases the right to legal representation that meets a certain standard of competence and performance. This right ensures that defendants receive help from attorneys who have the necessary skills, knowledge, and resources to defend their cases adequately, which is vital for a fair trial. When this right is violated, it can lead to wrongful convictions or unfair trials, underscoring the importance of competent legal counsel in the justice system.