"internal migration" meaning in English

{
  "forms": [
    {
      "form": "internal migrations",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "internal migration (countable and uncountable, plural internal migrations)",
      "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": "topical",
          "langcode": "en",
          "name": "Geography",
          "orig": "en:Geography",
          "parents": [
            "Earth sciences",
            "Sciences",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Permanent movement within a particular country"
      ],
      "id": "en-internal_migration-en-noun-zzdwjKyb",
      "links": [
        [
          "geography",
          "geography"
        ]
      ],
      "raw_glosses": [
        "(geography) Permanent movement within a particular country"
      ],
      "tags": [
        "countable",
        "uncountable"
      ],
      "topics": [
        "geography",
        "natural-sciences"
      ],
      "translations": [
        {
          "code": "fi",
          "lang": "Finnish",
          "sense": "Translations",
          "word": "maassamuutto"
        }
      ]
    }
  ],
  "word": "internal migration"
}

{
  "forms": [
    {
      "form": "internal migrations",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "internal migration (countable and uncountable, plural internal migrations)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English uncountable nouns",
        "Translation table header lacks gloss",
        "en:Geography"
      ],
      "glosses": [
        "Permanent movement within a particular country"
      ],
      "links": [
        [
          "geography",
          "geography"
        ]
      ],
      "raw_glosses": [
        "(geography) Permanent movement within a particular country"
      ],
      "tags": [
        "countable",
        "uncountable"
      ],
      "topics": [
        "geography",
        "natural-sciences"
      ]
    }
  ],
  "translations": [
    {
      "code": "fi",
      "lang": "Finnish",
      "sense": "Translations",
      "word": "maassamuutto"
    }
  ],
  "word": "internal migration"
}