What is the meaning of the statement made by the Hadith scholars about a narrator: "Salih al-Hadith" (sound in Hadith), "Layyin al-Hadith" (lenient/weak in Hadith), or "Muqarib al-Hadith" (close/acceptable in Hadith)?

These phrases indicate the lowest degree among the levels of amendment [of a narrator's trustworthiness], where the narrations of those described by them are not to be used as sole proof. Al-Nawawi mentioned that "salih al-hadith" (acceptable in hadith) is written for consideration, and "layyin al-hadith" (pliant in hadith) means that he is criticized with something that does not disqualify him from being considered just. "Laysa bi-qawi" (not strong) means his hadith is written, but he is below the level of "layyin". Al-Khatib reported from Ibn Abi Hatim that the hadith of "salih al-hadith" is written for consideration, and "layyin al-hadith" is written and examined for consideration, and the hadith of "laysa bi-qawi" is written. As for "da'if al-hadith" (weak in hadith), his narration is considered and not discarded. However, "matruk al-hadith" (abandoned in hadith) or "kadhdhab" (a liar) means his hadith is discarded and not written.