The United States currently taxes its citizens, residents, and corporations on all income, no matter where earned. If Congress were to adopt a territorial system, U.S. taxpayers would only pay tax on income produced at home.
The United States currently employs a “worldwide” system of international taxation. Any U.S. person (including a U.S. corporation) is taxed on all income earned, no matter where in the world that income is derived. However, if a corporation earns income through a foreign subsidiary, that income is generally not taxed in the United States (i.e., “deferred”) until the income is distributed to the U.S. parent of the foreign subsidiary as a dividend (also known as “repatriating” foreign earnings). U.S. corporations are therefore able to defer the U.S. taxation of this income, provided they keep the funds offshore—potentially indefinitely. In other words, the generally “worldwide” system is, in practice, limited by the availability of deferral.
Today, most countries have switched to what is called a “territorial” system of international taxation. In a territorial system, a jurisdiction only levies a tax on income produced within the jurisdiction. The Blueprint put forth by House Republicans would switch to a territorial system, whereas the plans put forth by President Trump thus far have been silent on the subject. Note that this territoriality feature of the Republican tax reform proposal (i.e., giving up worldwide taxation), although related, is distinct from the border adjustability feature of the DBCFT.