The omission may be from the start of the isnād by the compiler's action, this is al-muʿallaq.
Al-mursal is an omission from the end of the isnād, after the tābiʿī; one of the four kinds of rejected report rooted in a break in the chain.
An omission of two or more consecutive narrators at any point in the chain is al-muʿḍal, one of the four kinds of rejected report rooted in a break in the chain.
The rejected report falls into two kinds: that rejected because of an omission in the isnād, and that rejected because of criticism of the narrator.
A ḥadīth in which a narrator has been replaced with another, whether one narrator, several, or even the entire chain, is al-maqlūb (literally, that which has been inverted).
