"surface libre" meaning in Français

{
  "categories": [
    {
      "kind": "other",
      "name": "Compositions en français",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Locutions nominales en français",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Néologismes recommandés en français",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Traductions en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Traductions en croate",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Français",
      "orig": "français",
      "parents": [],
      "source": "w"
    }
  ],
  "etymology_texts": [
    "Locutioncomposée de surface et de libre."
  ],
  "forms": [
    {
      "form": "surfaces libres",
      "tags": [
        "plural"
      ]
    }
  ],
  "lang": "Français",
  "lang_code": "fr",
  "pos": "noun",
  "pos_title": "Locution nominale",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Lexique en français de l’hydrologie",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Lieu des points d'une nappe où la pression de l'eau est égale à la pression atmosphérique."
      ],
      "id": "fr-surface_libre-fr-noun-92Vk-Xe7",
      "topics": [
        "hydrology"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\syʁ.fas libʁ\\"
    }
  ],
  "tags": [
    "feminine"
  ],
  "translations": [
    {
      "lang": "Anglais",
      "lang_code": "en",
      "word": "free surface"
    },
    {
      "lang": "Croate",
      "lang_code": "hr",
      "word": "ploština slobodne površine tekućine"
    }
  ],
  "word": "surface libre"
}

{
  "categories": [
    "Compositions en français",
    "Locutions nominales en français",
    "Néologismes recommandés en français",
    "Traductions en anglais",
    "Traductions en croate",
    "français"
  ],
  "etymology_texts": [
    "Locutioncomposée de surface et de libre."
  ],
  "forms": [
    {
      "form": "surfaces libres",
      "tags": [
        "plural"
      ]
    }
  ],
  "lang": "Français",
  "lang_code": "fr",
  "pos": "noun",
  "pos_title": "Locution nominale",
  "senses": [
    {
      "categories": [
        "Lexique en français de l’hydrologie"
      ],
      "glosses": [
        "Lieu des points d'une nappe où la pression de l'eau est égale à la pression atmosphérique."
      ],
      "topics": [
        "hydrology"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\syʁ.fas libʁ\\"
    }
  ],
  "tags": [
    "feminine"
  ],
  "translations": [
    {
      "lang": "Anglais",
      "lang_code": "en",
      "word": "free surface"
    },
    {
      "lang": "Croate",
      "lang_code": "hr",
      "word": "ploština slobodne površine tekućine"
    }
  ],
  "word": "surface libre"
}