In Tajweed, "al-qalqalah" (القلقلة) refers to a rule of pronunciation for the Arabic letters that have a "heavy" sound. The term "qalqalah" means "shaking" or "vibration," and it refers to the way the tongue and throat vibrate when pronouncing these heavy letters.
The qalqalah letters are:
ق (Qaf)
ط (Taa)
ب (Ba)
ج (Jeem)
د (Dal)
When any of these qalqalah letters appear with a sukoon (a diacritical mark that indicates the absence of a vowel sound), and are followed by a vowel sound in the next syllable, the qalqalah rule applies. In this case, the letter is pronounced with a short, sharp "echo" sound, with a slight vibration of the tongue and throat.
For example, in the word "aqd" (عقْد), the letter "qaf" has a sukoon and is followed by the vowel sound "a." Therefore, the qalqalah rule applies, and the letter "qaf" is pronounced with a short, sharp sound, with a slight vibration of the tongue and throat.
The qalqalah rule is important in Tajweed because it helps to ensure the proper pronunciation of the heavy letters in the Quran, which is essential for reciting the Quran correctly and conveying its intended meaning. By following the qalqalah rule, the reciter can produce a clear and beautiful recitation that is pleasing to the ear and enhances the spiritual experience of the listener.