There are multiple types of client-side scripts: UI actions (if configured to run client-side), UI policies and UI policy actions, Client Scripts, and catalog Client Scripts (which are pretty much identical to client scripts, except that they run on catalog item forms, rather than regular ServiceNow forms that display a record.
Client Scripts are a specific kind of client-side script, which execute on forms (or in the case of onCellEdit Client Scripts, on the list view) of a record. Client Scripts come in four basic types: onLoad, onChange, onSubmit, and onCellEdit. Each type runs under different conditions, and often has a different use than the others.
