Polygamy means a system of marriage whereby one person has more than one spouse. Polygamy can be of two types. One is polygamy where a man marries more than one woman, and the other is polyandry, where a woman marries more than one man. In Islam, limited polygamy is permitted; whereas polyandry is completely prohibited.
The context of this phrase is the following verse from Surah Nisa of the Glorious Qur’an:
"Marry women of your choice, two, or three, or four; but if ye fear that ye shall not be able to deal justly (with them), then only one."