Riwāyat al-aqrān: Zayd narrates from a peer, ʿAmr; reverse narration is not required.
Mudabbaj: Those same two peers each narrate from the other.
Al-akābir ʿan al-aṣāghir: A senior teacher receives from a narrator junior in age, encounters, or standing.
Al-ābāʾ ʿan al-abnāʾ: A father narrates from his son, a specific senior-to-junior case.
Al-sābiq wa-l-lāḥiq: Two pupils share a teacher but their death dates differ markedly.
Each label addresses a different question: peerhood, reciprocity, seniority, family direction, or chronology. More than one may apply to a transmitter relationship if each has its own supporting evidence.