The K8s documentation describes containers and pods pretty well. But in essence:

A pod in the K8s context

• A group of containers
• Containers share networking. For example, the same IP address
• Typically multi-container pods are used when you need a sidecar container. For example:
  • A proxy process to your main container.
  • A debug container with utilities.
  • A process that always needs to run together with your app.
  • A container that does some sort of networking changes that your app needs.
• Allows you to set up a securityContext for all the pods in the container.
• Allows you to set up a Disruption Budget policy to prevent downtime for example.
• Allows you to use higher-level Kubernetes abstractions like Deployments, StatefulSets and Jobs.
• Allows you to set Pod presets so that a pattern can be reused.

A container in the K8s context

• A lower-level abstraction from a pod
• Allows you to specify the image
• Allows you to specify resources (mem/cpu)
• Allows you to setup Liveness, Startup, and Readiness Probes.
• Allows you to set up a securityContext just for the container individually