Showback is a feature in Calm that allows administrators to track and report the costs of running applications and projects on different cloud platforms. Showback can be enabled in the Setting menu of Calm, under the Showback tab. There, the administrator can configure the cost models, cloud accounts, and currency for Showback. Showback can also be accessed from the Dashboard menu, where the administrator can view the cost reports and charts for different applications and projects. Reference:
https://www.nutanix.com/support-services/training-certification/certifications/certification-details-nutanix-certified-professional-multicloud-automation-v6-5\
https://www.nutanix.com/content/dam/nutanix/resources/support/ebg-ncp-mca-6.pdf

A Brownfield Application is a type of application that allows you to import and manage existing VMs that were not deployed by Calm. You can use a Brownfield Application to perform actions such as start, stop, restart, delete, or execute scripts on the imported VMs. You can also add services, credentials, variables, and policies to the Brownfield Application blueprint. To create a Brownfield Application, you need to select a multi-VM blueprint and then choose the VMs that you want to include in the application from the drop down list. You can also filter the VMs by name, cluster, or power state.
A Greenfield Application is a type of application that allows you to deploy new VMs from scratch using Calm. You can use a Greenfield Application to provision and configure VMs on different cloud platforms, such as Nutanix AHV, VMware ESXi, AWS, Azure, or GCP. You can also add services, credentials, variables, and policies to the Greenfield Application blueprint. To create a Greenfield Application, you need to select a single-VM or a multi-VM blueprint and then specify the VM properties, such as name, image, flavor, network, storage, etc.
Reference:
Nutanix Calm DSL - Brownfield Apps the Easy Way
Nutanix Support & Insights
Getting started with Nutanix Calm

When launching Calm blueprints, there are two view options available: Developer and Consumer. The Developer view allows you to create, edit, and manage blueprints, as well as access advanced features such as macros, actions, and scripts. The Consumer view allows you to launch and manage applications from the Marketplace, as well as access basic features such as variables, tasks, and alerts. The view option is determined by the role assigned to the user in the project. Users with the Project Admin or Project Auditor role can switch between the Developer and Consumer views, while users with the Project User role can only access the Consumer view. Reference:
Nutanix Certified Professional - Multicloud Automation (NCP-MCA) v6.5, Section 1 - Describe and Differentiate Automation Concepts and Principles, page 3 Nutanix Multicloud Automation Administration (NMCAA), Module 2 - Nutanix Calm, Lesson 2.1 - Nutanix Calm Overview, page 9 Nutanix Calm User Guide, Introduction to Nutanix Calm, Nutanix Calm User Interface

Runtime variables are variables that can be modified by the Consumer during the deployment of a Blueprint or after the deployment is complete. They allow the Consumer to customize the attributes of the infrastructure and applications according to their needs. Runtime variables can be defined in the Blueprint settings or in the Blueprint YAML file. They can also be used in the Blueprint tasks to pass dynamic values to the scripts or commands. Runtime variables can be of different types, such as text, number, boolean, list, or password. They can also have default values, constraints, and descriptions to guide the Consumer.
Reference:
Nutanix Certified Professional - Multicloud Automation (NCP-MCA) Exam Blueprint Guide, Section 2, Objective 2.1 Nutanix Multicloud Automation Administration (NMCAA) Course, Module 4, Lesson 4.3 Nutanix Calm User Guide, Chapter 4, Section 4.2