I'd opt for a rather neutral descriptor that doesn't attach any positive or negative connotations to the approach. Particularly if you're completing a comparison exercise whereby the pro's and con's of each approach should be outlined.
I've used 'customized' and 'bespoke' as neutral descriptors for something that's not a traditionally recognized methodology but is, through either tried and tested experience or to fulfill the specific needs of the organisation that uses it, an existing approach.
In my opinion there is no development without the methodology. Development process always has some rules by which it is built. Even if seemingly there are no rules, "no rules" is also a rule. If you have one of that kind of process with minimal regulation, it looks like "Cowboy coding", where developers have minimum constraint from developing process.
You can also use CMMI definition of level 1 maturity:
Level 1 - Initial (Chaotic)
It is characteristic of processes at this level that they are (typically) undocumented and in a state of dynamic change, tending to be driven in an ad hoc, uncontrolled and reactive manner by users or events. This provides a chaotic or unstable environment for the processes.
It means, "for this"; the processes have been created specifically for the situation at hand. It can also rock, especially for small teams. I've worked with a lot of start-ups and find their processes tend to be more similar to Lean Start-Up than any other methodology, especially if you start including metrics for the artifacts you're producing and their use.
Commonly consists of a little documentation knocked up on a wiki, co-ordination of work through Google Docs or a whiteboard rather than an electronic project tool, and a higher focus on delivery over estimation and prediction compared to Agile.