Those are both official Disney sites, but the tickets are for two different Disney Resorts, Disneyland, which is located in Anaheim, California, and Disney World, which is located in Orlando, Florida.
There are many options for tickets in both complexes, but typically tickets either allow access to one park per day (the cheaper option), or are "park-hopper" tickets that allow switching between parks within a day. Obviously for one day tickets the former is equivalent to buying a ticket to a single park.
Disney World
Is by far the larger resort, and includes the Magic Kingdom Park, the Epcot centre, Hollywood Studios, the Animal Kingdom Park and the Water Park.
Disneyland
Includes Disneyland Park and Disney California Adventure Park. It most closely resembles the Magic Kingdom part of Disney World though there are several differences.
