How do you define self-serve product marketing? How is it different from "regular" product marketing?

For starters, I don't think self-service is separate from or comparable to "regular" product marketing. Self service should be an integral part of the infrastructure you form when looking forward and thinking about scaling. The goal of self-service is to help you scale, the idea behind it being that you empower stakeholders with the content, information, knowledge, etc. that they need in order for them to perform their jobs - without having to be "on call" for it to happen. 

Basically this means making it well known where the single source of truth is for positioning and messaging, and then also making clear what people can or cannot do with that information independently, based on your processes and policies. 

One example of implementation can be:

1. Create a positioning & messaging "encyclopedia" where you maintain a living breathing document of your core approach. 
2. In parallel, decide what your stakeholders can do with this info, write it down in a clear SOP format and store it wherever SOPs are stored and/or adjacent to the "encyclopedia". 
3. Announce, announce again, and announce at every opportunity the existence of said document + SOP.  

Two example use cases include empowering individuals to: 

• Create their own content and then send it to the PMMs for review and approval
• Learn about positioning and messaging and use it as a reference in their day-to-day

Self-serve product marketing is an approach to product marketing that focuses on empowering customers to find and use a product on their own, without the need for direct interaction with a sales team. 

This approach is often used for b2c products that are designed to be easy to use and understand, and that can be accessed and purchased without sales touch. This comes to positioning, messaging, GTMs, and content collaterals that will be different for self-serve vs sales-led. For example, self-serve positioning typically involves highlighting the user-friendly nature of the product, as well as its accessibility and ease of use.

While what is called "regular" product marketing has a more generalistic focus.

TDLR: self-serve product marketing focuses on the individual user persona and their use cases vs traditional product marketing in a sales-led company focuses on the buyer persona and business results. 

However, the catch is that most PLG organizations have both product-led growth and product-led sales happening simultaneously so you'll need both to have a successful acquisition strategy amongst SMB, Mid Market, and Enterprise alike! 

If you want more detail, check out this talk I did on the difference between PLG PMM and Sales-led PMM: https://youtu.be/Mbd0pUO1HXs