What are the letters of Ikhfah?

Ikhfah is a term used in Tajweed, the rules of Quranic recitation, referring to a specific way of pronouncing certain letters when they occur in certain contexts. The letters of Ikhfah are 15 in total: ت (Ta), ث (Tha), ج (Jim), چ (Cha), د (Dal), ذ (Thal), ز (Zay), س (Seen), ش (Sheen), ص (Sad), ض (Dad), ط (Ta), ظ (Zha), ل (Lam), and ن (Noon). When a Noon Saakin (ن) or Tanween occurs before any of these letters, the sound is pronounced with a nasal quality without fully merging or clearly enunciating the following letter.