Short for 'traditional', and in music it names traditional jazz — the older New Orleans style that was popular in the 1920s, where one instrument (usually the clarinet, or the trumpet leading) runs a busy, decorated line while the others hold a steady beat underneath. It is especially a British word: in 1950s and 60s Britain there was a whole 'trad jazz' revival, and 'trad' became the everyday name for that sound.

Short for 'traditional'是「traditional」的縮寫, and in music it names traditional jazz在音樂上指的是traditional jazz（傳統爵士樂） — the older New Orleans style that was popular in the 1920s也就是1920年代流行、比較早期的紐奧良風格, where one instrument (usually the clarinet, or the trumpet leading) runs a busy, decorated line由一項樂器（通常是單簧管，或帶頭的小號）演奏忙碌、裝飾性強的旋律線 while the others hold a steady beat underneath其他樂器則在底下維持穩定的節奏。It is especially a British word這特別是個英式用字: in 1950s and 60s Britain there was a whole 'trad jazz' revival1950、60年代的英國曾掀起一整波「trad jazz」復興, and 'trad' became the everyday name for that sound「trad」也就成了那種音樂的日常說法。

You will also hear 'trad' in British folk music, meaning a song so old that nobody owns it — the credit on the record just reads 'Trad.' More broadly, and this is worth knowing because you'll meet it online, people now use 'trad' as a casual adjective for anything old-fashioned or done the old way, sometimes warmly and sometimes as a joke; in the last few years it has also picked up a political flavour in some corners of the internet, meaning traditional in a social or religious sense.

You will also hear 'trad' in British folk music你也會在英式民謠裡聽到「trad」, meaning a song so old that nobody owns it意思是一首老到沒有人擁有版權的歌 — the credit on the record just reads 'Trad.'唱片上的作者欄就只寫「Trad.」 More broadly, and this is worth knowing because you'll meet it online更廣泛一點，這點值得知道，因為你會在網路上遇到, people now use 'trad' as a casual adjective for anything old-fashioned or done the old way現在大家會把「trad」當成隨口說的形容詞，指任何老派、用舊方法做的東西, sometimes warmly and sometimes as a joke有時候是善意的，有時候只是開玩笑; in the last few years it has also picked up a political flavour in some corners of the internet這幾年它在網路上某些角落也染上了政治色彩, meaning traditional in a social or religious sense指的是社會或宗教意義上的「傳統」。

The music sense is the settled, respectable one.

The music sense音樂上的這個意思 is the settled, respectable one才是穩固、正經的用法。