What is "wasla"

A Wasla , "joining sign" or more exactly, alifu lwasl (اَلِفُ الْوَصْلِ): Alif conjuctionis: ٱ, is a orthographical symbol or diacritic in the Arabic language, that is used to indicate liaison with the preceding word, and which suppresses the hamza in the sentence. Thus the movent hamza (al-hamzat ulmutaḥarrika) is inhibited and the two words are joined ("wasl"). Recently alif ulwasl is sometimes not written, though this incorrect.