Enterprise application, ASP.NET 3.5 framework, Vivek Thakur's architecture, complex system design, layered architecture, presentation layer, business logic layer, data access layer, entity framework, ADO.NET, Windows Server, IIS, cloud computing, virtual machines, scalable infrastructure, high availability, load balancing, clustering, firewall security, encryption, secure authentication, user authorization, role-based access control, database modeling, relational database, SQL Server, stored procedures, T-SQL, data warehousing, business intelligence, reporting services, dashboard analytics, system monitoring, performance optimization, caching mechanisms, content delivery networks.