Autoencoders are a type of neural network that can be used for dimensionality reduction in structured data. They consist of an encoder and a decoder, where the encoder compresses the input data into a lower-dimensional representation (encoding), and the decoder reconstructs the original input data from the compressed representation. By doing so, autoencoders can learn a compressed representation of the input data that captures the most important features while discarding noise and irrelevant information. This makes them useful for dimensionality reduction tasks, where reducing the number of input features can improve efficiency and performance.