The Throw Element is used to throw an exception and it takes an expression as a parameter.

When used with an HTTP or API Trigger, it can be configured to send an HTTP response or an HTTP binary response.

In the Process below, theTrigger Element is an HTTP trigger, and Throw Element comes after an Exclusive Decision Element returns a 404 error.

If an exception is not caught, the Process execution will end in an error state.
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If you have set a Subprocess to call on unhandled errors in a Process and use the Throw Element, you can toggle the 'Bypass Call Subprocess' option in the Throw Element's Parameter Editor.

The next article is Example on How to use Subprocess to call on an unhandled error.