There are several options possible.
You can configure the smart search index to do not cover given page type or location at all. You can set it e.g. as excluded content.
You can configure the search results web part and use search condition and exclude those items based on some flag, e.g. the -nodeclassID: 123.
You can use global event handlers and use the API to set the "Exclude from search" flag using the code.
If you mean search like Google or other search engines on the Internet, use robots.txt.