In this sense, networking is the practice of meeting people who do the same kind of work, or work that touches yours, so you can share news, help each other, and stay in one another's minds. It is less 'making friends for fun' and more 'building a useful circle.' People do it at conferences, after talks, on work trips, and on websites made for jobs. Business English likes this word; some speakers find it a bit shiny or forced, and would rather say they are meeting people in their field. You can use it as a noun (she is good at networking) or a verb (to network). It is not rude, but if you only talk to someone because they might be useful later, it can feel cold — and people notice. Though actually, the same spelling is also the everyday word for linking computers so they can share data. That is a different meaning. Here we mean people, not cables.