The term is metaphorically for someone who says a lot of things, without the actual knowledge backing it up.
The phrase is strongly associated with older generations, mostly baby boomers.
Origin of the term
The origin of the expression can be linked to Plato, who himself said, that “The empty vessel makes the greatest sound.”
Its first record in the English language was made by William Shakespeare, in his work called Henry V.
It has been used as an idiom, ever since.
Spread of the term
Its most notable use in modern day happened in 2017, when White House Chief of Staff John Kelly called a member of the Congress an empty barrel.
His comment gained great attention, mostly because of the shrouded sense of the expression, not understood by everyone, leading to articles being written about the incident.
The first Urban Dictionary entry was added on the idiom in the same year, alongside with several others, explaining it to those who are unversed in the thoughts of Plato.