Updated: Oct 5, 2019
Throughout my career working with many new artists and writers it still surprises me when I would mention the words 'Topline' and 'Production', which is more often than not followed with the question "what is the topline and what's the difference between that and the production?"
Topline: A topline covers everything that basically isn't the production - this would be the lyrics, vocal melodies, songwriting structure and the lyrical context. There are no rules whatsoever when writing toplines, though of course through practice a GREAT topline can be written.
Toplines are what DJ's always look for as their job is solely production - so when publishers are pitching a topline for DJ's, this will be the topline alone with very basic instrumental, like an acoustic guitar or keys. Sometimes it may even be accapella. If you want to really focus on what a topline is, listen to accapella's - this is the whole package of what a topline is as there is no production at all.
Production: Opposite to the topline, the production is everything the producer creates and records on tracks, including instruments, synths, vocals, production structure, effects, pitches, keys, tones, just to name a few. The list of what production entails is quite endless.
Artists and Topliners usually will be on the hunt for finding a great instrumental for them to topline on and make their own, and this is very common for big artists who have the right vocal hook, but struggling to find the most fitting production.
When working with professional songwriters, producers, publishers and record label executives, you'll hear these terms a lot when it comes to sessions and general songwriting development as it's a way of pinpointing the songwriters strengths so they are able to set up sessions / collaborations with the right people (e.g. two topliners - one who is an excellent lyricist another who is great with melodies and sings, plus one producer. All Topliners have different strengths so it's always common for there to be different types in a session. Three co-writers is the most common but there is never a limit. Some songs even have up to nine co-writers!)
On Publishing and some Record rosters you will find the list of writers / artists with the title 'Topliner' or 'Producer' or sometimes both if they're an "All-Rounder'" - another common term for songwriters who are great at both and are usually an A&R's dream for sessions as they can just dive straight into the session and work with every co-writer.
Ideally, it's great to know whether you're more of a topliner, producer, or all-rounder, but at the early stages it's not to worry if you're unsure of which category you fit best with.
As you develop, your weaknesses will become strengths and the strengths you already had to begin with will become even greater. It's common for producers to start out as just producers, but after many sessions they begin to find their voice and want to get in on toplines and build this, vice versa with topliners wanting to build their production skills.
The main thing is that writers are aware of the Topline vs Production terms in order to pinpoint the difference and know what a topliner should make their focus as well as a producer knowing what their focus should be. For All-Rounders, they've got the whole puzzle to fit together, but of course everyone has their weaknesses and should they need some more focus on the lyrics, or recording, they would know they'll need specially a topliner or producer, and not just the next general songwriter they come across.