"jam session" meaning in Anglais

{
  "categories": [
    {
      "kind": "other",
      "name": "Compositions en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Dates manquantes en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Locutions nominales en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Anglais",
      "orig": "anglais",
      "parents": [],
      "source": "w"
    }
  ],
  "etymology_texts": [
    "(Date à préciser)Composé de jam et de session."
  ],
  "forms": [
    {
      "form": "jam sessions",
      "ipas": [
        "\\ˈdʒæm ˈsɛʃ.ənz\\"
      ],
      "tags": [
        "plural"
      ]
    }
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "noun",
  "pos_title": "Locution nominale",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Lexique en anglais de la musique",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Bœuf, improvisation musicale."
      ],
      "id": "fr-jam_session-en-noun-q2nLHT55",
      "topics": [
        "music"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\ˈdʒæm ˈsɛʃ.ən\\"
    }
  ],
  "word": "jam session"
}

{
  "categories": [
    "Compositions en anglais",
    "Dates manquantes en anglais",
    "Locutions nominales en anglais",
    "anglais"
  ],
  "etymology_texts": [
    "(Date à préciser)Composé de jam et de session."
  ],
  "forms": [
    {
      "form": "jam sessions",
      "ipas": [
        "\\ˈdʒæm ˈsɛʃ.ənz\\"
      ],
      "tags": [
        "plural"
      ]
    }
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "noun",
  "pos_title": "Locution nominale",
  "senses": [
    {
      "categories": [
        "Lexique en anglais de la musique"
      ],
      "glosses": [
        "Bœuf, improvisation musicale."
      ],
      "topics": [
        "music"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\ˈdʒæm ˈsɛʃ.ən\\"
    }
  ],
  "word": "jam session"
}