A diploid reproductive cell undergoes meiosis to produce 4 haploid cells. It could be thought of as the diploid cells undergoing mitosis twice where the diploid cell divides into two, and then those two daughter cells divide again to become 4 daughter cells.
The only difference being that meiosis is similar to mitosis, but has the processes of independent segregation and crossing over occurring within the cells to introduce variation within the haploid daughter cells.