Dimension
In a vector space  (with vectors being "arrows" with directions), the dimension of , also written as , is equal to the cardinality (or number of vectors) of a basis of  (a set which indicates how many unique directions  actually has). It is also equal to the number of the largest group of straight line directions of that space. "Normal" objects in everyday life are specified by three dimensions, which are usually called length, width and depth. Mathematicians call this concept Euclidean space.