"We're open to English the way people really talk as opposed to what the textbooks say," Kelly said.
SLANGuage's purpose is to help students from abroad, who make up about 15 percent of Penn's enrollment, feel comfortable in their new environment and communicate in social settings. Kelly said he hadn't heard of this type of informal class at other universities. Christian Association executive director Rob Gurnee called it unique.
While participants may ask whatever they want about English, the class is not about the crass lingo that many think of as slang. SLANGuage is as much about culture as it is about words.
"We're not telling people what to believe, but we're trying to explain American culture," Kelly said, adding that the class often focused on holidays, popular music, comics, and the news of the day.
Sometimes the conversation does turn to campus jargon. Long Yun, 45, who was a visiting scholar at Penn's Annenberg School last year and attended 30 SLANGuage classes, said learning slang had helped her in her formal studies.
"So when Bill taught us the popular words hook up, I got it quickly and used it to describe the current cultural phenomenon," she wrote in an e-mail from her home city, Beijing, where she teaches at the Communication University of China.
A recent class, which included Kelly's 400th student, started with a discussion of Thanksgiving and the differences between religious and secular holidays. Emphasizing the importance of family during the holiday, Kelly said he had taken his grandchildren to the new Harry Potter movie and to the battleship in Camden over the weekend. One student shared that he was helping to create an Urdu version of the Encyclopedia of Islam. (Remember the board?)
As in many of the classes, the topics bounced around, this time from the life of musician Karen Carpenter, as the students listened to her version of "When I Fall in Love," to elections in Egypt. Most subjects are lighthearted; a student commented on the beauty of Carpenter's voice. But the mention of Egypt proved controversial for a student from that region.
"Once in a while, we get into a topic that's very sensitive, and I think we've done that today," Kelly said with a chuckle as he switched the topic to Christmas.
Partway through the discussion, Kelly offered beverages, and one of the red cans was met with a quizzical look. "It's Coca-Cola, the generic version," he assured the student.
Kelly's class has drawn students from 20 countries. Muhammad Arshad, a scholar from Pakistan who studies modernization and Islam in South Asia, called the class "very wonderful" and said he enjoyed English, especially listening to native speakers.
Although he had never left Pakistan until coming to the United States in September - after turning down a fellowship at Oxford - Arshad, 48, said he was happy to be "Americanized."
"Now I'm here, and I focus on here," he said with a smile.
In addition to teaching idioms such as "beat around the bush" and "keeping up with the Joneses," Kelly brings a touch of humor to his lessons. Yealing Lee, who grew up in Taiwan and received a master of business administration from Pennsylvania State University before moving to Philadelphia for her husband's studies, remembered when Kelly showed his donor card during a discussion of organ donation.
"On the back of the card, he added few words: 'Just make sure I am really dead,' " said Lee, who has attended SLANGuage more than 50 times.
Slanguage is not specific to Kelly's class. The term commonly refers to the words, phrases and dialects people use in a particular city, such as saying "wooder" for "water" in Philadelphia.
Mike Ellis of Kimberton, who founded Slanguage.com in 1995, said he started the site after his book on Philadelphia slang, Philly Fun-Ics, sold 40,000 copies.
"I just wanted to know, 'What did people say in other cities?' " Ellis said. "It got a lot of traffic right away. People really loved it."
Starting with just a few phrases on each page, the site has grown to incorporate cities around the world. Although it was primarily intended for an American audience, Ellis said, 60 to 70 percent of the site's traffic comes from abroad. He is responding to the international trend with books to help Americans learn foreign slanguage.
Like Ellis, who said slanguage could give people "confidence," Kelly values the difference a few key phrases can make in communicating.
"I have been in other countries, and people have helped me," Kelly said.
After often walking by the Christian Association when his wife worked near Penn's campus, Kelly went in one day and met with then-director Beverly Dale. The class evolved out of Kelly's interests, with Dale's support.
Kelly, who described himself as "internationally oriented," received a doctorate in economics and enjoyed a career researching the science and technology of the Soviet Union. He had a Fulbright fellowship in Minsk, Belarus, in 1993 and is now a full-time volunteer with Christ Presbyterian Church in Marlton, which has hosted refugees from Uzbekistan.
"Language is like a puzzle for me," Kelly said, describing his love of learning new languages as almost "crazy."
"I tell my wife, I don't go to bars and I don't play golf, so it could be worse," he joked.
Contact staff writer Liz Gormisky at 215-854-2917 or email@example.com.