ServiceNow Form Messages | Show messages as an Alert, Confirm, Info or Error messages from a Script

What are the different types of form message you can add on a form in ServiceNow? What do they mean and how to apply them using a client script or business rule.

Here we look at both form and field messages on client and server side scripting. https://docs.servicenow.com/en-US/bundle/utah-application-development/page/script/general-scripting/reference/r_ScriptingAlertInfoAndErrorMsgs.html