A newb is someone that is new to a certain industry.
There are other words alongside newb that mean the same thing, such as newbie, noob or nub. This is a slang term for a novice or a newcomer. Contemporary use can particularly refer to a beginner or new user.
At one point in your life, even you were a newb. Before you clicked on this to read it, you were a newb when it came to understanding its meaning, but now you are a pro.
You can think of this word as the meaning behind someone who is genuinely just getting into something new. This can be compared to the word "freshman" in college, which refers to someone who is a first-year student and does not really know what awaits them.
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