"happy vowel" meaning in English

{
  "etymology_text": "From its appearance at the end of the word happy.",
  "forms": [
    {
      "form": "happy vowels",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "happy vowel (plural happy vowels)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Phonemes",
          "orig": "en:Phonemes",
          "parents": [
            "Phonology",
            "Linguistics",
            "Language",
            "Social sciences",
            "Communication",
            "Sciences",
            "Society",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A vowel in spoken English that falls between /iː/ and /ɪ/ and may be represented by /i/."
      ],
      "id": "en-happy_vowel-en-noun-C6XoPR2V",
      "links": [
        [
          "vowel",
          "vowel"
        ],
        [
          "English",
          "English"
        ]
      ],
      "related": [
        {
          "word": "schwi"
        }
      ]
    }
  ],
  "word": "happy vowel"
}

{
  "etymology_text": "From its appearance at the end of the word happy.",
  "forms": [
    {
      "form": "happy vowels",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "happy vowel (plural happy vowels)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "schwi"
    }
  ],
  "senses": [
    {
      "categories": [
        "English autological terms",
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Phonemes"
      ],
      "glosses": [
        "A vowel in spoken English that falls between /iː/ and /ɪ/ and may be represented by /i/."
      ],
      "links": [
        [
          "vowel",
          "vowel"
        ],
        [
          "English",
          "English"
        ]
      ]
    }
  ],
  "word": "happy vowel"
}