Both actually. A niche site is usually centered around a specific topic. Content can be created manually or scraped and repurposed. The idea is to provide relevant transactional information and lead the user towards the conversion funnel which could be display ad, affiliate offer or any other sales pitch.
For instance, currently I am working on a website related to a coffee machine brand. I did the keyword and competition research, layout the site structure and monetization funnel. Now my team of writers is busy in creating content with the goal to turn out 30-40 highly quality content pieces in a month - enough to test the potential of the niche.
Another project I did previously was to set up mini sites for lawyers in a US state. I scraped existing lawyer directories to provide a lead management system to the client who then pitched development services to those without websites.