Ana is a mathmatical / philosophical term which can be best described as the 4th-dimensional equivalent to up in 3 dimensional geometry. Its opposite is kata. Ana and kata are like up and down, and can collectively be described as "the directions you can't point in". It's useful to define these when trying to visualise 4-dimensional geometrical shapes such as a hypersphere. Note that here, the 4th dimension simply refers to another geometrical dimension, not time.