What is the meaning of "ṭabaqah" (layer/class) and the phrase "in every ṭabaqah of the chains of narration" in the well-known definition of ḥadīth, along with examples to clarify this?

"Isnad strata refer to the stages of the chain of transmission through which a Hadith was narrated, such as the Companions, the Tabi'un (Successors), and their followers. An example of this is the Hadith about the Prophet's qunut (supplication), which was narrated from him by a group of Companions, including Anas and Ibn Abbas. From Anas, it was narrated by a group, including Qatadah and Abu Mijlaz, and similarly, narrators continued in each stratum in large numbers that did not fall short of the number for common report (shuhra)."