What is the definition of a Service object?

I found another definition for a service object instead that one described as an interface for concrete classes that are about to provide a certain service through that API definition set by the interface.

Article about Microservices >Link definition for service object:

3: Many object-oriented designers, including ourselves, use the term service object in the Domain-Driven Design sense for an object that carries out a significant process that isn't tied to an entity. This is a different concept to how we're using "service" in this article. Sadly the term service has both meanings and we have to live with the polyseme.

What I understand here its not the technical aspect like defining it as an "interface" but more the design concept it describes. I also understand an service object simply a domain of a class like its responsibility. So if you are developing web apps you might have a service object SecurityService which is a component of a SecurityController. The controller is calling the service to actually process security (the domain) specific services.

Domain-Driven Design defines a Service as:

A SERVICE is an operation offered as an interface that stands alone in the model, without encapsulating state... [p. 105]

Yes, it's a class with public methods, but in addition to that, it implements an interface that exposes those methods. At its core, the Service is the interface - the class that implements it is just an implementation detail.