In mathematics (and physics) a sequence of n numbers can be understood as a location in an n-dimensional space. When n=4, the set of all such locations is called the fourth dimension. Now, Mathematicians create videos that help in visualizing four-dimensional objects.
The 4th dimension may be interpreted either as time, or as a literal fourth dimension of space, a fourth spatial dimension. Rotating shadow of a tesseract rotating on a single axis and a single plane is fine example of 4th dimension.
From the article:
Three dimensions can be so limiting.
Mathematicians, freed in their imaginations from physical constraints, can conjure up descriptions of objects in many more dimensions than that. Points in a plane can be described with pairs of numbers, and points in space can be described with triples. Why not quadruples, or quintuples, or more?
You can watch all videos here online.