Conditional expressions are a key part of any programming language, allowing for return values to be determined based on true or false evaluations. In Terraform, conditional expressions are represented by the ternary operator and can be applied to various objects such as resources, data sources, outputs, and modules. Conditional expressions provide flexibility and re-usability in Terraform configurations by enabling them to adapt to different environments, requirements, or scenarios. The ternary operator is used to define a Boolean condition, a value when the condition is true, and a value when the condition is false. It can be applied to any parameter of a resource, data source, output, or local variable. Conditional expressions are useful for testing for the existence of a variable's value, configuring settings differently based on certain conditions, creating powerful logic to control whether to create a resource, filtering data, and returning values based on conditions. When used in combination with `count` and `for_each`, conditional expressions can be used to control whether a resource is created and how many instances of a resource to create. The use of logical operators such as && (AND), || (OR), and ! (NOT) allows for complex logic to be created when combining conditional expressions. However, there are limitations to using conditional expressions in Terraform, including not being able to apply them to providers and having limitations with module support. It is recommended to follow best practices such as avoiding complex conditions, using descriptive variable names, testing each conditional expression, and exploring alternative tools like Spacelift for managing Terraform infrastructure.