A tesseract is a four-dimensional geometric shape, also known as a hypercube. Just as a cube is a three-dimensional version of a square, a tesseract extends this concept into the fourth dimension. It can be visualized as a cube that has been "stretched" into an additional dimension, making it difficult to fully comprehend since we live in a three-dimensional world. In mathematics and physics, tesseracts are used to explore concepts of higher dimensions and can help in understanding complex theories, such as those in string theory or theoretical physics. They are often represented in two or three dimensions through projections, similar to how a three-dimensional object can be represented in two dimensions.