The terms are often used interchangeably, but they’re not the same. Here’s the difference:
Deep web. This is a part of the internet that doesn’t show up on conventional search engines — basically, it includes unindexed web pages like pages hidden behind paywalls, medical records, and email accounts. So, this is the internet that search engines can’t access.
Dark web. This is a part of the deep web that is intentionally hidden and is fully encrypted. Regular search engines can’t access it — it can only be accessed via the Tor browser.