The dagesh (דָּגֵשׁ) is a diacritic used in the Hebrew alphabet. It was added to the Hebrew orthography at the same time as the Masoretic system of niqqud (vowel points). It takes the form of a dot placed inside a Hebrew letter and has the effect of modifying the sound in one of two ways.
An identical mark called mappiq, carrying a different phonetic function, may be applied to different consonants; the same mark is also employed in the vowel shuruq.
Dagesh and mappiq symbols are often omitted in writing. For instance, בּ is often written as ב. The use or omission of such marks is usually consistent throughout any given context. The two functions of dagesh are distinguished as either kal (light) or hazak (strong).
Read more about Dagesh: Dagesh Kal, Dagesh Hazak, Rafe, Unicode Encodings