Deep learning is a subset of machine learning that employs artificial neural networks to learn from data, achieving breakthroughs in fields such as computer vision, natural language processing, and speech recognition. It utilizes architectures like convolutional and recurrent neural networks to model and process complex data, while optimization techniques such as gradient descent and backpropagation are pivotal for training. The advancements in computational power and availability of large datasets have fueled the rise of deep learning applications across various domains.