A ‘top only’ jingle is a version of the jingle where there is sung vocals at the very start and the rest is a music bed (or instrumental) so that a voice over may be heard. It is similar to a top and tail but without the tail. Like every jingle cut, a top only jingle has its purpose in the right context. The sung vocals at the very start effectively introduces your business name or product without taking up a lot of time, which then allows a lot more time for the spoken message to be heard.
For more definitions, read the post jingle lingo, what does it all mean.