Homologous chromosomes

Homologous chromosomes are pairs of chromosomes within diploid cells that share the same structure and gene arrangement (same genes at the same loci).
Homologous chromosomes may possess different versions (alleles) of the same genes.
In other words, homologous chromosomes represent a "set" of chromosomes in a diploid cell.
Homologous chromosomes pair up during prophase I in meiosis to form bivalents.

Reduction Division

Meiosis is a nuclear division that produces haploid cells from a diploid cell.
Diploid cells have two of each type of chromosome. Haploid cells only have one of each type of chromosome.
Meiosis is known as a reduction division because the daughter cells are haploid whereas the parent cells are diploid. In other words, the total number of chromosomes reduces by half.
A reduction division maintains the original chromosome number during fertilisation.
For example a human cell has 46 chromosomes. Gametes only contain 23 chromosomes. When an egg and a sperm fuse to form a zygote, the number of chromosomes returns to 46.