The most common and most likely answer to this crossword clue is the 12 letter word GOBBLEDYGOOK
I've seen this crossword clue in The Times
G
O
B
B
L
E
D
Y
G
O
O
K
More clues leading to the result GOBBLEDYGOOK
Buddy explains!

The straight part
We know that "Jargon" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jargon = gobbledygook.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 GOBBLEDYGOOK mean?
GOBBLEDYGOOK noun- Nonsense; meaningless or encrypted language.
- Something written in an overly complex, incoherent, or incomprehensible manner.