Lateral reading means: “instead of digging deep into the site at hand...lateral readers don’t spend time on the page or site until they’ve first gotten their bearings by looking at what other sites and resources say about the source at which they are looking... they get off the page...they open up many tabs in their browser.
From Caulfield, M. A. (2017). Web Literacy for Student Fact-Checkers. https://collection.bccampus.ca/textbooks/web-literacy-for-student-fact-checkers-361/
GO WIDE: Lateral reading is a strategy for investigating who's behind an unfamiliar online source by leaving the webpage and opening a new browser tab to see what trusted websites say about the unknown source. It helps you determine an author’s credibility, intent and biases by searching for articles on the same topic by other writers (to see how they are covering it) and for other articles by the author you’re checking on. It's one of the primary strategies employed by professional fact checkers.
The lateral reading concept and the term itself developed from research conducted by the Stanford History Education Group (SHEG), led by Sam Wineburg, founder and executive director of SHEG.
Read More: Expand Your View with Lateral Reading from the News Literacy Project.
Let’s look at this study that was done at Stanford in 2017, where 45 individuals were observed evaluating live websites and searching for information on social and political issues. The participants in the study were 10 Ph.D. historians, 10 professional fact checkers, and 25 Stanford University undergraduates.
One of the tasks these participants were given was to look at these two websites to determine which one was more credible (selecting the image below will take you to the home page of each organization):
American Academy of Pediatrics 
American College of Pediatricians
One of the websites is an American professional association of pediatricians, headquartered in Itasca, Illinois. It has 67,000 members. It has the largest pediatric publishing program in the world, with more than 300 titles for consumers and over 500 titles for physicians and other health-care professionals.
The other site is a socially conservative advocacy group of pediatricians and other healthcare professionals in the United States. In 2016 it reportedly had around 500 members. The group's primary focus is advocating against abortion and the adoption of children by gay or lesbian people. It also advocates conversion therapy. It’s been listed as a hate group by the Southern Law Poverty Center and others.
Clearly these two are very different, even though it’s hard to tell by looking at these websites. They both appear very similar and very professional, or at least have a veneer of professionalism.
So which of the websites did the participants decide was more credible?
Amazingly, 65% of the Stanford students actually chose the hate site as the more credible site, and 50% of the historians failed as well to determine which was more credible.
But the fact-checkers -guess how they did with this task? Turn out 100%, or ALL of the fact checkers were able to determine which site was more credible. In addition, they were able to do so within seconds, compared to the other groups that took the whole time given to make a decision. The secret behind their success? Lateral reading.
Wineburg, S., & McGrew, S. (2017). Lateral Reading: Reading Less and Learning More When Evaluating Digital Information (SSRN Scholarly Paper 3048994). https://doi.org/10.2139/ssrn.3048994
