Input data refers to the information or signals that are fed into a system for processing. This data can come from various sources, such as sensors, user inputs, or databases. In computing, input data is essential for algorithms and programs to perform tasks and generate outputs. In the context of machine learning, input data is used to train models, allowing them to learn patterns and make predictions. The quality and relevance of the input data significantly impact the performance of the model, making it crucial to select and preprocess it carefully before use.