What is the overall purpose of meiosis?

In short: Meiosis makes sure that the offspring is a different individual compared to its parents.

Meiosis is specialised cell division which occurs in all sexually reproducing organisms. The purpose of meiosis is to reduce chromosome number by half (diploid (2n) to haploid (n)) which occurs thanks to two consecutive cell divisions (meiosis I and meiosis II) without DNA multiplication in between. What's particularly important about meiosis is the so called crossing-over process which allows an exchange of homologues segments between homologues chromosomes. This exchange of information results in a recombination of information.