The most common and most likely answer to this crossword clue is the 7 letter word GAMELAN
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More clues leading to the result GAMELAN
Buddy explains!

The straight part
We know that "Indonesian orchestra" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case indonesian orchestra = gamelan.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GAMELAN mean?
GAMELAN noun- A genre of music of Indonesian origin typically featuring metallophones, xylophones, drums, gongs and a bamboo flute (called a siuling).
- The name of the ensemble performing this style of music.