I just had someone ask me what negative keywords really mean, so let me just make a post about it. Google adwords works by targeting keywords your potential customers might be typing in, but it also can target any keyword someone might type in.
So a negative keyword, will be one that won’t produce results, because it doesn’t have any potential buy intent.
“blue flowers” – this could be a negative keyword, because you don’t know if someone is looking for pictures of blue flowers, or they are looking to buy blue flowers. As it can go either way, it’s good idea to add it as a negative, else it can drain a whole lot of your budget if you go broad and don’t have a set of good negative keywords to avoid your paid ads showing up on words that have low chance of producing results.