►II.8. GEMINATE CONSONANTS
This diacritic ّ◌ (the dotted circle ◌ is not part of the diacritic) is called šadda·t شَدَّةٌ “stress”. It indicates geminate letters, i.e. two identical consonants with no vowel in between.
م + م = مّ
m + m = mm
Geminate consonants are called lengthened consonants.
Click on the following Arabic words to hear how they are pronounced: