(uncountable) Gas generated in the digestive tract.
This expression is utterly devoid of meaning, a mere flatus vocis.
(countable) Expulsion of such gas through the anus.
(obsolete) Morbid inflation or swelling.
1730 April, Jonathan Swift, "A Vindication of the Lord Carteret", in Thomas Sheridan and John Nichols (Eds.), The Works of the Rev. Jonathan Swift, D.D., Dean of St. Patrick’s, Dublin, Volume IX, J. Johnson &c. (1801), page 226,
[…] an incensed political surgeon, who is not in much renown for his mercy, upon great provocations: who, without waiting for his death, will flay and dissect him alive; and to the view of mankind lay open all the disordered cells of his brain, the venom of his tongue, the corruption of his heart, and spots and flatuses of his spleen: and all this for threepence.