They talk a lot about balloons! (7)
I believe the answer is:
gasbags
'balloons' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Perhaps they are linked in a way I don't understand?
'they talk a lot' is the wordplay.
'they talk' becomes 'gas' (I can't explain this - if you can you should believe this answer much more).
'a lot' becomes 'bags' (bags can mean a large amount).
'gas'+'bags'='GASBAGS'
'about' acts as a link.
Can you help me to learn more?
(Another definition for gasbags that I've seen is " Talkative people".)