Convolutional neural networks are a type of artificial neural network used for processing pixel data, especially for image recognition and processing tasks. They are composed of convolution layers that perform feature extraction using kernels, pooling layers that perform downsampling, and fully connected layers that map extracted features to outputs. CNNs have advantages like local connections, weight sharing, and dimensionality reduction. They are widely used for applications like image recognition, video analysis, natural language processing, anomaly detection, drug discovery, game playing, and time series forecasting.