Level AA is a little more significant, and makes sites accessible to people with a wider range of disabilities, including the most common barriers to use. It won't impact the look and feel of the site as much as Level AAA compliance, though it does include guidance on color contrast and error identification. Most businesses should be aiming for Level AA conformity, and it appears to reflect the level of accessibility the DOJ expects. 
These and other types of multimedia can present two distinct problems for people with different disabilities. People who are deaf or hard of hearing can generally see the information presented on webpages. But a deaf person or someone who is hard of hearing may not be able to hear the audio track of a video. On the other hand, persons who are blind or have low vision are frequently unable to see the video images but can hear the audio track.
The Department of Justice’s revised regulations for Titles II and III of the Americans with Disabilities Act of 1990 (ADA) were published in the Federal Register on September 15, 2010. These regulations adopted revised, enforceable accessibility standards called the 2010 ADA Standards for Accessible Design, "2010 Standards." On March 15, 2012, compliance with the 2010 Standards was required for new construction and alterations under Titles II and III. March 15, 2012, is also the compliance date for using the 2010 Standards for program accessibility and barrier removal.
Develop a plan for making your existing web content accessible. Describe your plan on an accessible webpage, and encourage input on how accessibility can be improved. Let visitors to your website know about the standards or guidelines that you are using to make your website accessible. When setting timeframes for accessibility modifications to your website, make more popular webpages a priority. 

The debate over the Americans with Disabilities Act led some religious groups to take opposite positions.[32] The Association of Christian Schools International, opposed the ADA in its original form.[33] primarily because the ADA labeled religious institutions "public accommodations", and thus would have required churches to make costly structural changes to ensure access for all.[34] The cost argument advanced by ACSI and others prevailed in keeping religious institutions from being labeled as "public accommodations".[24]
If posted on an accessible website, tax forms need to be available to people with disabilities in an accessible format on the same terms that they are available to other members of the public – 24 hours a day, seven days a week, without cost, inconvenience, or delay. A staffed telephone line that sent copies of tax forms to callers through the mail would not provide equal access to people with disabilities because of the delay involved in mailing the forms.
Enough Time: Users have sufficient time to read and use the website’s content. If part of the website has a time limit, users are able to turn off the time limit, or they can adjust or extend it to at least ten times the default limit (unless the time limit is essential to the website’s functionality, such as auction websites like eBay). Content that moves, blinks, or automatically updates can be paused or stopped unless it’s essential to the website’s functionality.
The Americans with Disabilities Act (ADA) was first passed in 1990. Twenty years later, the US Department of Justice released an update called the 2010 ADA Standards for Accessible Design. These standards cover the design of physical spaces and have been interpreted to include web locations as well, so it can be difficult for the would-be accessible website designer to use them.

Olmstead v. L.C.[65] was a case before the United States Supreme Court in 1999. The two plaintiffs L.C. and E.W. were institutionalized in Georgia for diagnosed mental retardation and schizophrenia. Clinical assessments by the state determined that the plaintiffs could be appropriately treated in a community setting rather than the state institution. The plaintiffs sued the state of Georgia and the institution for being inappropriately treated and housed in the institutional setting rather than being treated in one of the state's community based treatment facilities.

Under Title III, no individual may be discriminated against on the basis of disability with regards to the full and equal enjoyment of the goods, services, facilities, or accommodations of any place of public accommodation by any person who owns, leases, or operates a place of public accommodation. Public accommodations include most places of lodging (such as inns and hotels), recreation, transportation, education, and dining, along with stores, care providers, and places of public displays.

For most people, the Americans with Disabilities Act (ADA) conjures up pictures of physical accommodations such as wheelchair ramps near building entrances, handicapped parking spaces, and the use of braille writing on signs and placards. These measures have been tremendously valuable in helping the 56.7 million Americans with a disability function and thrive within society.

The ADA itself holds different organizations to more/less stringent standards based on a host of factors, government funding being a major one. Government agencies themselves are usually held to the most severe standards. That said, while ADA has adopted WCAG as the defacto standard, from what I’ve seen it appears they’re going with AA compliance as the most reliable one. That said, we’ve done work with some organizations who’ve chosen to comply with AAA in an effort to be as buttoned up as possible from an accessibility and experiential perspective. We’ve also worked with some who have tighter budgers and aim for level A compliance and have a more “react and repair” mindset when they discover anything in their site that is giving someone hardship from an accessibilirt standpoint.

Title II of the ADA prohibits discrimination against qualified individuals with disabilities in all programs, activities, and services of public entities. It applies to all state and local governments, their departments and agencies, and any other instrumentalities or special purpose districts of state or local governments. It clarifies the requirements of section 504 of the Rehabilitation Act of 1973, as amended, for public transportation systems that receive federal financial assistance, and extends coverage to all public entities that provide public transportation, whether or not they receive federal financial assistance. It establishes detailed standards for the operation of public transit systems, including commuter and intercity rail (e.g., AMTRAK).