In the 21st century, journalism is often defined by what it isn’t, rather than what it is. This is, sadly, the case for many professions that are not widely esteemed by the general public.
Journalism is further complicated by the fact that there are more breeds and types of it than living creatures in a rain forest. For example, there is good journalism, bad journalism, mediocre journalism, lazy journalism, press release journalism, hack journalism, government journalism, non-profit journalism, for-profit journalism, print journalism, broadcast journalism, community journalism, sports journalism, and investigative journalism, just to name a few types.
For the sake of defining the term, we will simply acknowledge with a sigh that both good journalism and bad journalism, though they are separated by a wide gulf, are both journalism.
So, at its most basic level, journalism, however one practices it, is simply the conveying of new information to the public. Some journalists will do this well, others will do it horribly enough that it takes four or five editors to make sense of it, and others will actually win awards (given to them by other journalists, of course, as the profession is not appreciated by anyone outside of journalism) for doing an exceptional job at informing the public.