"َ" meaning in Arabic

{
  "forms": [
    {
      "form": "ـَ",
      "tags": [
        "canonical"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "ar",
        "2": "letter",
        "head": "ـَ"
      },
      "expansion": "ـَ • (-a)",
      "name": "head"
    }
  ],
  "lang": "Arabic",
  "lang_code": "ar",
  "pos": "character",
  "senses": [
    {
      "categories": [
        {
          "kind": "topical",
          "name": "Arabic diacritical marks",
          "parents": [
            "Diacritical marks",
            "Letters, symbols, and punctuation",
            "Symbols",
            "Orthography",
            "Writing",
            "Human behaviour",
            "Language",
            "Human",
            "Communication",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Arabic entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "fatḥa (فَتْحَة), indicates a short /a/ or its cognates, indicates a long /aː/ if followed by an ا (ʔalif)."
      ],
      "id": "en-َ-ar-character-fBDYQWMM",
      "links": [
        [
          "fatḥa",
          "fatḥa"
        ],
        [
          "فَتْحَة",
          "فتحة#Arabic"
        ],
        [
          "ا",
          "ا#Arabic"
        ]
      ],
      "tags": [
        "letter"
      ]
    }
  ],
  "word": "َ"
}

{
  "forms": [
    {
      "form": "ـَ",
      "tags": [
        "canonical"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "ar",
        "2": "letter",
        "head": "ـَ"
      },
      "expansion": "ـَ • (-a)",
      "name": "head"
    }
  ],
  "lang": "Arabic",
  "lang_code": "ar",
  "pos": "character",
  "senses": [
    {
      "categories": [
        "Arabic diacritical marks",
        "Arabic entries with incorrect language header",
        "Arabic lemmas",
        "Arabic letters"
      ],
      "glosses": [
        "fatḥa (فَتْحَة), indicates a short /a/ or its cognates, indicates a long /aː/ if followed by an ا (ʔalif)."
      ],
      "links": [
        [
          "fatḥa",
          "fatḥa"
        ],
        [
          "فَتْحَة",
          "فتحة#Arabic"
        ],
        [
          "ا",
          "ا#Arabic"
        ]
      ],
      "tags": [
        "letter"
      ]
    }
  ],
  "word": "َ"
}

{
  "called_from": "form_descriptions/1698",
  "msg": "unrecognized head form: -a",
  "path": [
    "َ"
  ],
  "section": "Arabic",
  "subsection": "letter",
  "title": "َ",
  "trace": ""
}