If your Jenkins server sits behind a firewall and does not have the direct access to the internet, and if your server JVM is not configured appropriately (See JDK networking properties for more details) to enable internet connection, you can specify the HTTP proxy server name in this field to allow Jenkins to install plugins on behalf of you. Note that Jenkins uses HTTPS to communicate with the update center to download plugins.

The value you submit here will be set as `http.proxyHost` system property. Leaving this field empty causes this property to be unset, which means Jenkins will try to connect to the host directly.

If you are unsure about the value, check the browser proxy configuration.