I smiled reading James Sheasby Thomas’s (@rightsaidjames) post on how we collect pointless or esoteric domain knowledge from testing software. 
I have a rudimentary knowledge of shipbroking. Not enough to get a job at a shipbroking firm, but I reckon I could still talk you through a graph of VLCC charter rates and how that relates to the cost of oil.
Skillz! 
Read of the full post. It’s brilliant!
How about you, what’s the most niche domain knowledge you’ve gained from testing software? 
For anyone interested, 2006 me could share how to use two different statistical models and multiple datasets to come to a single property price valuation, with confidence indicator. Ooh, sounds fancy!
To be honest though, that was such a long time ago I’d have no idea where to start – but at the very least I know who I could contact to remind me. 
Maybe that’s the point of the forgotten or flaky esoteric domain knowledge. We build connections with people who we could at least call on if we needed them.
One of the domain knowledge that I have learned through software testing is banking. In my previous company, I worked on an app that used Stripe as a payment gateway, and now, while at my current organization, which is Fin-Tech, I have learned more about how the banking sector works, the risks involved, and the rules that apply.
It’s been really interesting to see that testing is no longer just about checking dropdowns and input fields but also making sure financial transactions follow the right rules and regulations.
It also helps in realizing that testing is not just about finding bugs but also understanding the bigger picture of security and trust in financial tech.
A whole bunch of random domain knowledge: population genomics (usage of genomic data to identify the possibility of cancers, revisiting my childhood dreams of becoming a doctor), medical imaging (stared at the images long enough to again think of oncology), tested CRM for an apartment management company where I learnt a lot of real estate and leasing terms and workflow and learnt about random towns in USA which I had not set foot at that time in.
In my previous company I tested eye imaging devices; taking images of the back of the eye with a laser (seeing the layers of the retina). So now every time I go to my optician or optometrist, I can have a semi-informed conversation 
.
My current employer provides positioning correction services, to provide better positioning results for satellite navigation (to name just one use case). I always like to talk to people that satellite navigation 
out of the box only can provide an accuracy up to 3 metres; and then go and explain the technologies used (and challenges faced with that) to provide more accurate (to cm level) positioning 
.
Guess not many of us know that increased ionospheric activity (yes, the beautiful Northern Lights) can massively throw off positioning results correctness.
Got a few gems of domain knowledge, in no particular order:
I worked on websites for US real estate. I got to know how the centralised the system was because you could fetch details about properties by using a unique ID assigned to them. These IDs would also be used by marketing companies to upload marketing material for your property.
And the marketing company was something, it was called Homevisit and boy did they know how to work a magic. They had 3D tours, HD video and photography and what not. The client wanted us to make the website responsive from screen sizes as small as an iPhone 6 to as large as a 4K tv.