Literally: thousand – say – ten thousand – word
Alternately: Very many words. A vast number of words. Really quite a very large number of words indeed. Speech or writing that is long-winded, meandering, overdone, prolix, repetitive, tedious, verbose, and/or, well, wordy.
Notes: 千 and 万 are both common examples than can simply mean “a very large number or amount” rather than one or ten thousand specifically. There are quite a few yojijukugo that use them, either in the form 千A万B as above, or in the form XY千万, to express “a whole lot of [something].”
In this particular compound, 万 can also be pronounced as man without being strictly wrong, but ban is far more common and is the preferred reading.
This phrase comes to us from the poetic words, I mean works, of late Tang era poet Zheng Gu (鄭谷, Japanese Teikoku).