user38458: Bitcoin "regtest" is for when you want to run a local version of Bitcoin where the state is only shared within a small community, whereas both "mainnet" and "testnet" are shared with the rest of the world.
I get why its called "mainnet" and "testnet", but where does the word "regtest" come from?

user38458: It stands for "regression test". As you can see here:

Regtest
Regression test mode
A local testing environment in which developers can almost instantly
generate blocks on demand for testing events, and can create private
satoshis with no real-world value.

https://developer.bitcoin.org/glossary.html?highlight=regression

38458: <p>Bitcoin &quot;regtest&quot; is for when you want to run a local version of Bitcoin where the state is only shared within a small community, whereas both &quot;mainnet&quot; and &quot;testnet&quot; are shared with the rest of the world.</p>
<p>I get why its called &quot;mainnet&quot; and &quot;testnet&quot;, but where does the word &quot;regtest&quot; come from?</p>
 38458: <p>It stands for &quot;regression test&quot;. As you can see here:</p>
<blockquote>
<p><strong>Regtest</strong></p>
<p><strong>Regression test mode</strong></p>
<p>A local testing environment in which developers can almost instantly
generate blocks on demand for testing events, and can create private
satoshis with no real-world value.</p>
</blockquote>
<p><a href="https://developer.bitcoin.org/glossary.html?highlight=regression" rel="nofollow noreferrer">https://developer.bitcoin.org/glossary.html?highlight=regression</a></p>
