An inconsequential numerical amount.
In 1999, Gonzalez received $1.4 million from the National Institutes of Health to compare his enzyme-nutritional therapy with the best chemotherapy now available for the treatment of advanced pancreatic cancer. As a percentage of the fifteen billion dollars that the federal government spends on medical research annually, the grant amounts to what one federal health official described to me as "decimal dust."
Michael Specter, "The Outlaw Doctor," The New Yorker, February 5, 2001
Critics worry that as partnerships bloom, they could drain billions of tax dollars from the Treasury, and even lead to the "disincorporation" of America. The Treasury Department originally estimated it could raise $665 million over a five-year span by changing the tax status.
The Stanger Report dismisses that revenue estimate as exaggerated, saying revised Treasury studies now say the government would gain just $24 million next year if it taxes MLPs as corporations "decimal dust," as one senator put it.
Stephen Maita, "The Bloom is Off the MLP Market," The San Francisco Chronicle, July 27, 1987
Something (usually a dollar amount) gets called decimal dust after it has been compared to something much larger. For example, consider the numbers in the citation above: Dividing the $1.4 million received by the doctor with the $15 billion medical research budget, the result is 0.000093. That tiny decimal fraction makes the smaller monetary amount seem almost nonexistent, as though it could be blown away like a speck of dust.