Homologous chromosomes (homologs) are chromosome pairs, both containing the same set of genes. They are of the same size (the exception being sex chromosomes), and their centromeres are in the same position. The chromosomes pair up during meiosis, to produce four, non-identical gametes.
Each chromosome pair contains the genes which code for the same features, but can either contain the same, or different alleles. One copy of the chromosome is inherited from the father, and one from the mother.
In a genetically normal human, there are 22 pairs of autosomal chromosomes and one pair of sex chromosomes - 46 chromosomes in total.
The ploidy of an organism is the number of homologous versions is has of each chromosome.