Mitosis

Ordinary cell division
Same number of chromosomes in new cells
New cells identical to parent cell
For growth
For asexual reproduction
In body cells

Meiosis

Reduction cell division
Half the number of chromosomes
New cells different mix of chromosomes and genes
For making gametes
For sexual reproduction
In reproductive organs

Chromosomes are threads of DNA which carry the genetic material (genes). In humans there are 23 pairs of chromosomes. In sex chromosomes there are only half the number.