What is a diploid organism?
Diploid organism is one which contain 1 set of homologous chromosomes.
Diploid organism is defined as organism with 1 set of homologous chromosome, i.e., organism has two copies of same gene in the system.
humans for example has 23 pairs of homologous chromosomes, with 2 copies of each gene on two chromosomes. denoted as 2n.
The figure shows karyogram for human male. where you can see set of 23 pairs of homologous chromosomes.