Tesseract is like a 4-dimensional cube. Instead of having three sides with length, width, and height, tesseract has four sides, with length, width, height and time. Imagine a cube with eight corners. Tesseract looks like this cube, but with 16 corners. It's like a cube with four extra sides. All these sides are connected in a way, so it looks like a box with four sides. Time is like a fourth dimension that can make the cube change in shape and size. So tesseract is a kind of cube with four sides, with length, width, height, and time, that can change its shape and size.