Which of the following best describes Application Containers?

Application containers are best described as encapsulations that allow for a single service operation. This definition highlights the primary function and advantage of containers in software development and deployment. Containers package an application and its dependencies together, ensuring that it runs consistently across various computing environments. This encapsulation enables the application to operate independently, isolated from other applications and the host system, which is particularly beneficial for microservices architectures.

Containers streamline the deployment process by providing environments that contain everything needed for the application to function, leading to simplified scaling and management. By allowing for single service operation, containers enhance efficiency and agility in development, as developers can focus on individual microservices without concern for the broader operating environment.

Other options may point to related concepts but do not accurately describe the specific function of application containers. Tools requiring an external server suggest dependency on infrastructure that doesn't capture the essence of containerization. Platforms for running database services tend to focus more on data management solutions rather than the service encapsulation aspect of containers. Combinations of multiple applications do not reflect the singular focus of containers on one application or service, which is a fundamental characteristic of their design.