What is the difference between performing a procedure on a resource and performing a state transformation?

I'm new to web development and I'm attempting to understand the notion of REST, and have been watching tutorials to help with this.

The tutorial I'm watching makes mention of the difference between "procedures" and "state transformation". Stating that REST is based on the notion of "state transformation", but it does not delineate the difference between the two. This has left me wondering why can't an operation which transforms the state of a resource also be considered a procedure? After all, 'procedure' sounds like a generic enough term that it would also encompass an operation that would transform the state of a resource.

What is the difference between performing a procedure on a resource, and performing a state transformation? Or is it merely a matter of semantics?

I have also tried searching for the answer but can't seem to find anything that will shed light on this.