The symbol "2n" refers to the total number of chromosomes that a diploid cell contains. Cells, in human and animal context, typically have either one or two sets of chromosomes, which store DNA. A single set of human chromosomes contains 23 chromosomes, so there are "2n", or 46, total cells in a haploid human cell.
Most cells in the human body are diploid, which means that they contain genetic information from both parents. However, sex cells, known as gametes, only have one set of 23 chromosomes, and are therefore haploid. Certain cells are known to have many sets of chromosomes; triploid cells have three sets, while heptaploid cells have seven sets.