If you’d like your ads to show on certain sites across the Internet, you can add these websites as:
The Correct Answer is:
A placement is a page from the website, a website, an individual ad unit positioned on a single page, a video, a mobile phone app or anything related to these.
These are the location on YouTube and display networks where your ad can be shown.
Placement targeting can help you place your ad at any specific location.
Google can also set automatic placement for you based on the keywords you or any other targeting method.