IRS

1.
Internal Revenue Service.
abbreviation
1.
(in the US) Internal Revenue Service
2.
insulin resistance syndrome: a condition associated with diabetes mellitus in which higher than normal levels of insulin are present in the blood to compensate for the failure of normal insulin levels to perform their function

also I.R.S., initialism of Internal Revenue Service, U.S. federal government tax collection agency, attested by 1954. The office dates to 1862; name changed 1953 from Bureau of Internal Revenue.
1.
infrared spectrograph
2.
Internal Revenue Service