The idea that you should help others before being concerned with your own needs. This does not, of course, apply to basic needs.
Cynically, the idea is that, to get what you want, you should give others what they want first and what you want will follow.
Application
In SEO
Google rewards sites that deliver the best user experience for a keyword with the highest ranking. If your goal is more relevant traffic, find the right keyword for your audience and deliver the best experience you can for that keyword.
Keep the user’s intent in mind and make sure they can get everything from your page, even if that means linking out to related links from competitors.