"Btb." meaning in English

{
  "forms": [
    {
      "form": "Btb.",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "Btb."
      },
      "expansion": "Btb. (plural Btb.)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "bass tuba"
        }
      ],
      "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 2 entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Music",
          "orig": "en:Music",
          "parents": [
            "Art",
            "Sound",
            "Culture",
            "Energy",
            "Society",
            "Nature",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Abbreviation of bass tuba."
      ],
      "id": "en-Btb.-en-noun-HONHvSQa",
      "links": [
        [
          "music",
          "music"
        ],
        [
          "bass tuba",
          "bass tuba#English"
        ]
      ],
      "raw_glosses": [
        "(music) Abbreviation of bass tuba."
      ],
      "tags": [
        "abbreviation",
        "alt-of"
      ],
      "topics": [
        "entertainment",
        "lifestyle",
        "music"
      ]
    }
  ],
  "word": "Btb."
}

{
  "forms": [
    {
      "form": "Btb.",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "Btb."
      },
      "expansion": "Btb. (plural Btb.)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "bass tuba"
        }
      ],
      "categories": [
        "English abbreviations",
        "English countable nouns",
        "English entries with incorrect language header",
        "English indeclinable nouns",
        "English lemmas",
        "English nouns",
        "English nouns with irregular plurals",
        "English palindromes",
        "English terms spelled with .",
        "English words without vowels",
        "Pages with 2 entries",
        "Pages with entries",
        "en:Music"
      ],
      "glosses": [
        "Abbreviation of bass tuba."
      ],
      "links": [
        [
          "music",
          "music"
        ],
        [
          "bass tuba",
          "bass tuba#English"
        ]
      ],
      "raw_glosses": [
        "(music) Abbreviation of bass tuba."
      ],
      "tags": [
        "abbreviation",
        "alt-of"
      ],
      "topics": [
        "entertainment",
        "lifestyle",
        "music"
      ]
    }
  ],
  "word": "Btb."
}