How would I refer to a person who says nothing in many words?

Question

What would be an appropriate term for a person who says a lot of things but conveys no useful information in saying them? I thought that this is a demagogy, but Wikipedia says that demagogy is proposing popular ideas rather than saying nothing with many words.

Summarizing the answers: The discussion here had decided that the answer is windbag. However, the difference between windbag and demagogue says that demagogue can be more appropriate if zero windbag "argument" successfully attracts the public opinion.

Answer 1

A person like this is sometimes referred to as a windbag. His talking is just the equivalent of "blowing wind;" that is, not meaningful.

Answer 2

Verbose: using or containing too many words; "long-winded (or windy) speakers"

Levin smiled joyfully; he was struck by this transition from the confused, verbose discussion with Pestsov and his brother to this laconic, clear, almost wordless communication of the most complex ideas.

Anna Karenina by Tolstoy, Leo

Garrulous: Given to excessive and often trivial or rambling talk; tiresomely talkative.

Often, when they had no more agreeable occupation at hand, the Misses Murray would amuse themselves with visiting the poor cottagers on their father's estate, to receive their flattering homage, or to hear the old stories or gossiping news of the garrulous old women

Agnes Grey by Bronte, Anne

Prolix: Tediously prolonged; wordy:

"The manner is indifferent," interrupted Inez, too anxious to await the prolix explanations of the old man; "why is the visit made?

The Prairie by Cooper, James Fenimore

An ineffectual speaker: Someone whose speech lacks forcefulness or effectiveness; weak

Or more simply a bore: One that is wearingly dull, repetitive, or tedious.

Answer 3

"Blatherer" and "blithering idiot" and "bloviator" are insulting terms for "a person who says nothing in many words".

Sometimes the job of a "diplomat" is to say "nothing in many words". On the other hand, sometimes the job of a diplomat is to be very clear and to the point.