Qalqala refers to vibrating certain letters in Arabic pronunciation when they have a Sukoon diacritic. Specifically, the letters that vibrate are ق, ط, ج, د, and ب. Examples show that these letters vibrate when they occur in the middle of a word with a Sukoon or at the end of an ayah/phrase when stopping on that letter, as the letter is treated as if it has a Sukoon. The document provides an activity where the reader drags the Qalqala letters into the word "Qalqala" and drags circles onto letters with Qalqala in examples.