I'm really glad you've asked this, Zeuhl. People are so happy to hide these terms, without realising that they're actually pretty meaningless.
Right-wing and Left-wing are umbrella terms - not much else. Both terms encompass hugely various (and often contradictory) belief systems. What unifies them varies in place to place.
I disagree with AOG's distinction. You can find just as many right-wingers who are eager for the state to interfere in peoples' lives as you can left-wingers - I don't think it's a particularly credible way to distinguish them. I think if there's any difference at all, it probably boils down to exactly what kind of state interference and means of social control are seen as legitimate and which are not. For example, someone of the 'right' is generally speaking pretty comfortable with the government intervening in peoples' lives in the name of "security" (whatever that may mean), whereas someone on the 'left' is normally pretty happy for the government to intervene in peoples' lives in the name of "social justice" (whatever that may mean) or some other end.
Of course, that's just in a British context. The meaning varies elsewhere.
To answer the question, "True Right/Left Wing" principles typically means whatever the speaker wishes it to mean. It is a meaningless umbrella term and a thinly disguised appeal to authority, and should be treated like the fallacy it is.
A good, classic essay on this subject is Oakeshott's 'Rationalism in Politics'. Personally, I think he made an excellent case for abandoning arbitrary Right-Left partisan obsessions altogether.