The Catch keyword is part of the Try/Catch exception-handling construct. See Try for more details on exception handling.
In the event of an exception being thrown within a Try/Catch block, program flow jumps to the Catch section matching the exception type; after the relevant error-handling code is executed, program flow exits the Try/Catch block.
Multiple Catch sections may be declared within a Try/Catch block in order to handle different types of exception. See Try for examples and further details.