Exceptions are unintended events that take place when a program is being executed or during its runtime causing disruptions to the program's overall logic. In Ruby, a program is enclosed between the begin and end blocks and a rescue block is used to tell what types of exceptions are to be handled. When no class is specified, by default, a RuntimeError is raised by Kernel#raise.

The ActionController::UnpermittedParameters error occurs when a parameter that has been passed is not permitted in a create, an update, or a user-defined action. In older versions of Rails, information about the unpermitted keys was provided in the logs only when an unpermitted parameter was found in a request. This did not provide enough information for the developers to understand which controller and action received the unpermitted parameters.

The urllib.error.HTTPError is a class in the Python urllib library that represents an HTTP error. An HTTPError is raised when an HTTP request returns a status code that represents an error, such as 4xx (client error) or 5xx (server error).

Exception handling is the process of responding to unwanted or unexpected events when a computer program runs. Exception handling deals with these events to avoid the program or system crashing, and without this process, exceptions would disrupt the normal operation of a program.

A runtime error is a type of error that occurs during program execution. The Python interpreter executes a script if it is syntactically correct. However, if it encounters an issue at runtime, which is not detected when the script is parsed, script execution may halt unexpectedly.

The io.netty.handler.timeout.ReadTimeoutException is a runtime exception in Java that is thrown when no data is read within a certain period of time when using the Netty framework. Since the io.netty.handler.timeout.ReadTimeoutException is thrown at runtime, it does not need to be declared in the throws clause of a method or constructor.

The java.util.concurrent.TimeoutException is a checked exception in Java that is thrown when a blocking operation times out. Since java.util.concurrent.TimeoutException is a checked exception, it must be explicitly handled in methods which can throw this exception - either by using a try-catch block or by throwing it using the throws clause.

The PHP E_WARNING constant refers to run-time warnings. Warnings are non-fatal errors in PHP that do not halt script execution.

The C# “an object reference is required for the non-static field” error is thrown when an object reference is required for the nonstatic field, method or property.. Install the C# SDK to identify and fix these errors.

Migration in Rails is a tool that allows the developer to use Ruby to change an application's database schema. Instead of using SQL scripts, we use Ruby code, which is database independent, so it is easy to move the application to a completely new platform. We define these database changes in domain-specific language (DSL), and these migrations can be rolled back and managed along with the application source code.