A classifier is a type of algorithm used in machine learning and artificial intelligence to categorize data into different classes or groups. It analyzes input data and assigns it to predefined categories based on learned patterns. Common examples of classifiers include decision trees, support vector machines, and neural networks. Classifiers are widely used in various applications, such as spam detection in emails, image recognition, and sentiment analysis in social media. By training on labeled datasets, classifiers improve their accuracy over time, making them essential tools in fields like data science, natural language processing, and computer vision.