Hullo and welcome!
Sadly, no simple statements. This subject of how to bring up poly with potential new squeezes has been discussed a lot just because there is no one catch word to sum it all up. Do a tag search on 'dating' and see what others have come up with.
As to the specific question of whether to describe the philosophy or the practice I would take the practice, and if further questions arise, make sure to mention 'polyamory', 'responsible non-monogamy', 'non-exclusiveness' or whatever you think describes your situation best. If they are interested, they will check out Google or Wikipedia, or ask you outright.
The biggest confusion I see people having is confusing responsible non-monogamy with cheating. Something quite casual like 'my boyfriend has been going on dates with this girl, and I think she's really cute and they seem to be getting on fine' or whatever circumvents the problem some people have with blurting out 'I'm polyamorous' or 'You need to know I have a live-in bf', since it doesn't always ring a bell and would imply that you are actually thinking this new thing is going to be a relationship. Cheating and seeking out affairs is something that makes culturally a lot more sense, as it were, so that is what people will automatically assume in most cases.
As to general aversion to labels - you need to establish a certain level of common language with anyone you meet in order to be mutually understood. It doesn't have to be polyamorous or boyfriend or a even a relationship, but something that even if it doesn't 100 % describe your life philosophy communicates something across the board. I lean towards 'ATM I'm dating someone but we are not exclusive', but there are really lots of ways people have chosen to tell the same thing. Read around a bit and see what feels right to you.
"Resentment destroys more alcoholics than anything else. From it stems the root of our spiritual disease."
"In dealing with resentments, we set them on paper - list people, institutions and principles with whom you are angry. Ask yourself why you are angry."
"In most cases it was found out that our self-esteem, our pocketbooks, our ambitions, our personal relationships, including sex, were hurt or threatened. We were sore, burnt-up." Alcoholics Anonymous, 64-65.