An alternate timeline is a reality that diverges from the "true" timeline due to the actions of time travellers or other temporal phenomena. In the Channel 27 universe, alternate timelines are named for who created them.
"Ron's World"[]
By Ron Weasley wishing that he had never been born:
Ernie didn't go back to school to get his GED.
Stan Shunpike andHagrid got arrested.
Harry Potter became friends with Draco Malfoy, didn't save Ginny Weasley, and became a Spanish teacher/Glee club sponsor.
Ginny Weasley died.
Professor Dumbledore was arrested after Ginny's death, and replaced with Professor Grumbly-Plank.
Hogwarts closed.
Hermione Granger becomes a librarian.
Professor Quirrell got the Soceror's Stone, and was able to back Lord Voldemort back.
Sirius Black didn't break out of Azkaban to defeat Peter Pettigrew.