Meaning of the requestAttribute?

From what I can see, you are calling an AEM Component, and passing the requestAttributes parameter to your Sling Model backend. 

If you are using Sling Model, from the backend, to capture the requestAttribute will be:

 @RequestAttribute
    private String href;

If you are using WCMUsePojo, from the backend, to capture the requestAttribute will be:

get("href", String.class);

You can see how to pass data from Sightly to Sling Model

How to Pass Data Parameters to Sling Modal from Sightly HTL Component

You can see how to pass data from Sightly to WCMUsePojo

How to Pass Data Parameters to WCMUsePojo from Sightly HTL Component

@RequestAttribute private String href;

@anasustic  Aslo ref. https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/requestattributes-data-sly-include/m-p/371183

<sly data-sly-use.settings="com.adobe.examples.htl.core.hashmap.Settings" data-sly-include="${ 'productdetails.html' @ requestAttributes=settings.settings}" / 

 And 'requestAttributes' can be passed from Java class.

public class Settings extends WCMUsePojo {

  // used to pass is requestAttributes to data-sly-resource
  public Map<String, Object> settings = new HashMap<String, Object>();

  @Override
  public void activate() throws Exception {
    settings.put("order", "ascending");
  }
}
@Model(adaptables=SlingHttpServletRequest.class)
public class ProductSettings {
  @Inject @Optional @Default(values="empty")
  public String order;

}
here 'order' is injected via the Map from the Use-class