Which component is required to host a GIS web application using ArcGIS Enterprise?

To host a GIS web application using ArcGIS Enterprise, ArcGIS Server is essential as it provides the necessary infrastructure to publish, share, and manage geospatial services for web applications. ArcGIS Server is designed specifically to serve data and analytical capabilities over the web, allowing users to access GIS resources via web applications. This server component enables the deployment of GIS content and offers features such as geocoding, routing, and spatial analysis services.

Other components mentioned, like ArcGIS Desktop and ArcGIS Pro, are primarily used for creating and managing geographic data rather than hosting web applications. ArcGIS Online is a cloud-based platform that complements ArcGIS Enterprise but is not required to host an application within the ArcGIS Enterprise environment. ArcGIS Server is, therefore, the critical component that consolidates these functionalities into a scalable platform for delivering web applications.