For some reason i’ve always had this question: is polyamory simply defined by being in a relationship with more than one people or it can also be used if someone isn’t in a relationship but actually feels romantic attraction for more than one?

Polyamory can be understood as as a behavior or sexual/relationship practice or as an identity/way of being. If you understand it as a behavior, then a person can be inclined toward polyamory, but the definition is more limited to the actual practice. If you understand it as an identity, then a person can be polyamorous no matter how many relationships they are or are not in. 

I personally experience my polyamory as a part of my identity, so I am polyamorous all of the time. If all my partners left me tomorrow and I was totally single, I would still be polyamorous. If all but one of my partners left me tomorrow and I was only dating one person, our relationship would still be polyamorous. Having the capacity to feel romantic attraction for multiple people is polyamory, even if you are not acting on it. Just like I am still straight even if I am not in a relationship or not currently being attracted to a sexy man right at this moment.