The dimensions field in the equation dialogue box is provided for reference only. It is not necessary to edit this information. The dimensions are a measure of the size of an array (or vector). Note that a vector is a one-dimensional array, and the term array is used here to cover both.
[2,3,4] has dimensions 3
[[2,3,4],[4,6,8]] has dimensions 2,3
In: Contents >> Working with equations