I assume you were watching The Network Trips OSPF series?
lol how did you know..!!?? yes exactly.
The wording "Empty Bridge interface" is exactly what Wilmer called it. And I had just watched that within the last week.
BTW, that is a good series in my opinion. There are some assumptions, i.e. that you understand networking fundamentals and how routing works (connected routes, how routes are selected, etc.). But the course (at least the first two I watched) are well organized, and he uses good practice (like the use of loopback interfaces). And his example shows the two most common types of links, and has 4 routers, so you get enough repetition to let the process sink in.
Here's another OSPF resource
MikroTik MTCRE - OSPF (An Introduction to a GIANT of a protocol!) by The Network Berg. When learning a new subject, watching several different presenters is a good thing as they will each probably cover some different things. Always verify what is said on a youtube video or some post you see. The Network Trip and The Network Berg are both good sources in general, and the Network Berg has some good information on all the requirements to getting an adjacency to come up. At this
point he discusses creating a loopback interface (which he names lo0), and why it is a good idea (the interface never goes down).