Phenomenon of equal prices without price collusion Some time ago, I came across a term describing a specific phenomenon observed in free markets. I'm now looking for this term.

When comparing prices of certain staples in some countries, one quickly notices that their prices are exactly the same in different supermarkets and discounters. For example, in Germany, the cheapest price for 1 kg of sugar in any supermarket or discounter is 65 ¢. I have never seen a different price for this for years. The exact brand of sugar is different for different supermarkets or discounters, but the cheapest offer is always 1 kg for 65 ¢. It's the same for eggs, milk, flour, yeast, salt, curd, and many other staples.

This price does not change as its in every competitor's interest to keep it exactly where it is:


If a market participant increases the price to make more money off the specific product, many people will avoid the supermarket or discounter because their prices are perceived to be higher in general as the staple in question serves as a price comparison between shops for many people.
If a market participant decreases the price to attract more customers, any competitor will decrease the price of their equivalent product to not appear to have higher prices than the participant that decreased their price.


This phenomenon results in supermarkets and discounters limiting the amount of a product customers can buy rather than increasing prices when running short of resupply or taking losses.

Note that I'm not looking for the term "price collusion". The term describes the exact phenomenon described above and does not suggest that price collusion is happening.

I'm not 100% sure this term exists in English. I only know that it exists in German because I read about this phenomenon on the German version of Wikipedia, but no one I asked in real life can tell me what it is. I guess that it exists in English, too, as it is an economic phenomenon not limited to any specific geographic region. Now I need the English term (if it exists) for usage in an English document.
I know you are at pains to say you are not looking for 'collusion' as an answer, but what you describe sounds very much like tacit collusion. Here's a quote from Competition Policy by Massimo Motta (pp138–140):


  I briefly characterise the concept of collusion from the point of view of industrial economics. Note that here I will not use the term "collusion" as a synonym for "collusive agreement that should be outlawed". Indeed, one of the main themes of this chapter is that whereas in economic theory collusion is defined as a market outcome (i.e., "high prices", in a sense to be specified further below), anti-trust authorities and judges should consider as illegal only practices where firms explicitly coordinate their actions to achieve a collusive outcome.
  
  [...]
  In economics, collusion is a situation where firms' prices are higher than some competitive benchmark. [...] In any case, in economics collusion coincides
  with an outcome (high-enough price), and not with the specific form through
  which that outcome is attained.
  
  [...] It is important to stress that [colluding firms need] not talk to each other, neither directly nor through intermediaries: collusive prices will arise through purely non-co-operative behaviour of the sellers. In other words, if detection of deviations is rapid, and if (market) punishments of deviations are likely and credible, then tacit collusion can arise: firms do not necessarily have to talk to each other, let alone agree on complicated schemes, for a collusive outcome to be sustainable. All that is needed is the awareness that a deviation will be identified, and that a "punishment" will follow.


The 'punishment' that Motta refers to is exactly the idea that, if one firm cuts its price to break the tacitly collusive status quo, other firms will 'punish' it by responding with a price cut of their own.

Sometimes, tacit collusion is known by the alternative name conscious parallelism to reflect the idea that firms are consciously mimicking each others' strategies. Particularly among legal scholars, the term conscious parallelism is used to mean coordination of prices without an agreement, whereas the term collusion is reserved specifically for the case in which an agreement has taken place. Among economists, as Motta explains above, both practices are known as (respectively, tacit and explicit) collusion and the conscious parallelism terminology is less common.