There are four versions of SharePoint Server 2010 as specified in following URL :
SharePoint Server 2010 Enterprise Client Access License features
For organizations looking to expand their business collaboration platform to enable advanced scenarios. Use the Enterprise capabilities of SharePoint to fully interoperate with external line-of-business applications, Web services, and Microsoft Office client applications; make better decisions with rich data visualization, dashboards, and advanced analytics; and build robust forms and workflow-based solutions.
SharePoint Server 2010 for Internet Sites, Enterprise
For organizations looking to create customer-facing public internet sites and private extranets using the full enterprise capabilities of SharePoint. This provides full SharePoint Enterprise functionality and no other technical limits.
SharePoint Server 2010 Standard Client Access License features
For organizations looking to deploy a business collaboration platform across all types of content. Use the core capabilities of SharePoint to manage content and business processes, find and share information and expertise, and simplify how people work together across organizational boundaries.
SharePoint Server 2010 for Internet Sites, Standard
For small and mid-sized organizations looking to create public Internet sites or basic extranets using the Standard features of SharePoint Server 2010.