Service Plans are available in different configurations.
Concurrent Users
This refers to the number of end users who can interact with your application at the same time.
Even if a Service Plan configuration does not set a limit on the number of concurrent users, you may find that there is a practical limit that your application can support, as discussed here.
Application Container
This defines the amount of memory available to each of the Service Plan’s Application Containers.
Lower amounts of memory are suitable for small to medium sized applications that typically do not server high numbers of concurrent users.
Scalable
Whether or not the Service Plan can be scaled.
Service Plan scaling allows additional Application Containers to be added to the Service Plan to meet an increasing number of concurrent end users. Adding additional Application Containers may impact the cost of a Service Plan.
Application Database
Whether or not a Service Plan includes one Application Database as part of its subscription.
Additional application databases can be added to a Service Plan, although this may impact the cost of the subscription.
Bandwidth
Some Service Plans may have their out-bound bandwidth artificially limited.
It is not recommended for Service Plans that will host production applications.