Deep learning is a subset of machine learning that involves the use of neural networks with many layers (hence the term "deep") to analyze and learn from large amounts of data. This technique allows for more complex and hierarchal representations of data, leading to higher accuracy in tasks such as image and speech recognition, natural language processing, and more. Deep learning has been increasingly popular in various industries, including healthcare, finance, and technology, due to its ability to automate and improve decision-making processes.