alt Hacker News1-2 bars isn't really espresso, it's a moka - which can be quite good in its own right. It falls into the genus of pressurized brewing though, so same genus different species. There's a no man's land from 3-5 bars that is not really used and might be worth exploring, but most 'standards' consider 6 bar the minimum to be a true espresso.
The SCAA (Specialty Coffee Association of America) has an even more restrictive definition[1]:
> Espresso is a 25–35ml (.85–1.2 ounce [×2 for double]) beverage prepared from 7–9 grams (14–18 grams for a double) of coffee through which clean water of 195°–205°F (90.5°–96.1°C) has been forced at 9–10 atmospheres of pressure, and where the grind of the coffee is such that the brew time is 20–30 seconds. While brewing, the flow of espresso will appear to have the viscosity of warm honey and the resulting beverage will exhibit a thick, dark golden crema.
I have no problem with calling soup espresso. It's ground coffee brewed under pressure in an espresso machine and that's good enough for me.
[1]:https://sca.coffee/sca-news/25-magazine/issue-3/defining-eve...