The Tax Code/Internal Revenue Code (IRC) is codified in Title 26 of the USC.
* Okay, Bloomberg has another tax page. We have Bloomberg Tax! That's great, because it's full of Intense Tax Stuff.
Abbreviations
IRC or I.R.C.: Internal Revenue Code aka Tax Code
USC or U.S.C.: United States Code
Prior Versions
There are prior versions of the IRC, namely in 1938, 1954, and 1986. You'll see them referenced as 'IRC of 1954,' for example. If you just see IRC listed, assume it's the current version.
Citations
ALWD
Bluebook