"free surface" meaning in All languages combined

{
  "categories": [
    {
      "kind": "other",
      "name": "Locutions nominales en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Anglais",
      "orig": "anglais",
      "parents": [],
      "source": "w"
    }
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "noun",
  "pos_title": "Locution nominale",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Lexique en anglais de l’hydrologie",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Surface libre."
      ],
      "id": "fr-free_surface-en-noun-FrAQ33N~",
      "topics": [
        "hydrology"
      ]
    }
  ],
  "word": "free surface"
}

{
  "categories": [
    "Locutions nominales en anglais",
    "anglais"
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "noun",
  "pos_title": "Locution nominale",
  "senses": [
    {
      "categories": [
        "Lexique en anglais de l’hydrologie"
      ],
      "glosses": [
        "Surface libre."
      ],
      "topics": [
        "hydrology"
      ]
    }
  ],
  "word": "free surface"
}