what is service block in BEM naming methodology?

BEM elements rules say.

https://en.bem.info/methodology/quick-start/

Create an element If a section of code can't be used separately without the parent entity (the block).

The exception is elements that must be divided into smaller parts – subelements – in order to simplify development. In the BEM methodology, you can't create elements of elements. In a case like this, instead of creating an element, you need to create a service block.

Question: can anyone tell me the meaning of service block in BEM?