Poly relationship or polyamory is a type of ethical non-monogamy. Poly relationships involve committed relationships, usually romantic relationships, between two or even more people.
Basically, if you ever find yourself as a part of a poly relationship, it means that you and your partner are both free to date other people if you like. It is important to remember that polygamy and polyamory are two different things. In polygamy, this involves being simultaneously married to several persons. Poly relationships are not automatically sexual in nature even though they can still be.