What is the meaning of Fatha?

In Arabic script, the vowel point for a, appearing as a diagonal line placed above a letter ( ـَ ) and designating a short a /a/. If the Arabic letters ا (‎أَلِف (ʔalif)) or ى (‎أَلِف مَقْصُورَة (ʔalif maqṣūra)) immediately follow, it indicates a long ā /aː/.

The vowel designated by this mark.