The ACA changed health insurance regulations, placing new requirements on most or all health insurance plans in the United States. These changes have resulted in the obsolescence of many existing plans, and the creation of many new plans. As a result of this, some number of individuals are no longer covered by their previous health care plans.
This is commonly in the media termed as people having "lost their insurance due to Obamacare". However, hard numbers are hard to come by. The top several search results all give different numbers, and many are obviously biased.
This site claims five million have lost coverage. The Kansas City Star claims as many as 52 million could lose coverage. CBS reports two million. California Health Line puts the number over seven million. All those numbers are at least a few months out of date, and I don't think I trust any of them even if they were current.
How many people that had health insurance have ceased to have health insurance, confirmably as a direct consequence of the ACA? How many of those now pay more for insurance? And how many of those would be eligible for Medicaid, but live in states that have elected not to accept the Medicaid expansions under the ACA?