Allaah (The Most high) said:
وَيْلٌ لِّكُلِّ هُمَزَةٍ لُّمَزَةٍ
[وَيْلٌ –Woe]; meaning, loss and destruction. And it is said [that it means] a valley in Jahannam.
[لِّكُلِّ هُمَزَةٍ لُّمَزَةٍ – to every slanderer and backbiter]; this is his preoccupation and practice (or habit), slander and backbiting -violating the honour of the people, speaking ill of them and defaming them. Slandering by way of speech and backbiting by way of action through indication (or gesturing). [End of Quote (Ref 1)]
Qaadhi Iyaad (rahimahullaah) stated that the word [وَيْلٌ –Woe] carries some of the following meanings: [a] It is used whilst referring to one who has fallen into destruction. [b] It is used whilst referring to one who deserves destruction. [c] It is used to refer to destruction itself. [d] It is used to refer to the difficulty found in punishment. [e] It is used to refer to grief. [f] It is used to refer to a valley in the hell fire. [Ref 2]
[Ref 1: Sharh Ad-Duroos Al-Muhimmah Li-Aammatil Ummah’ page 27’ by Shaikh Abdur-Razzaaq Al-Badr (may Allaah preserve him). Abridged & slightly paraphrased]
[Source: Quoted by Shaikh Abdullaah Al-Bukhaari (may Allaah preserve him) in Sharh Umdatul Ahkaam: lesson 2]