What is static resources in Salesforce?

It allows you to upload your content that you can reference in a Visualforce page.

It includes:-

• .zip and .jar files
• images style sheets
• JavaScript
• and other various files.

To reference a stand-alone file, use $Resource.<resource_name> as a merge field, In this <resource_name> is the name you specified when you uploaded the resource.

For Example,

<apex:image url=”{!$Resource.TestImage3}” width=”100″ height=”160″/>