An aggregator is a piece of software (or website) which collects news from other websites, blogs, podcasts and vlogs and makes them available all in one place. At one time these offered SEO opportunities and would rank quite highly in search results but too many websites used the concept purely as a way to get traffic for advertising revenue, rather than to act as a useful tool so Google and other search engines began marking them down. In principal, providing links to other, useful websites in your own content is good for SEO, but you need to put a little more effort in – simply running scripts to aggregate content will get your site penalised by search engines.