Peter Naylor, head of advertising sales at Hulu, stood on a stage before a roomful of advertising executives who were there to see what the popular streaming service had in store for the year. After trumpeting Hulu’s new interactive ads, Mr. Naylor made another pitch. “We offer you the opportunity to become part of the creative process with us,” he said.

Meaning what, exactly?

“Goose Island IPA has signed on to sponsor our hit series ‘Casual’ and integrate into the show,” Mr. Naylor said. And in the current season of “The Mindy Project,” he added, “not only does Mindy fall in love with her new Microsoft Surface Book, but she also gets to escape the city in her newly designed Lexus RX.”

This kind of advertising through product placement is certainly not new. But Mr. Naylor’s announcement — made during last week’s Digital Content NewFronts, an annual sales event where companies like Hulu compete for digital advertising dollars — underscored a broader question running through the advertising industry: What exactly constitutes an ad these days?

For decades, 30-second television commercials were the gold standard, and as online video proliferated, many digital ads were essentially repurposed from TV. But in the last several years, advertisers have become more sophisticated, creating digital ads that were divorced from traditional campaigns and were better suited to the many platforms that have become available, including Facebook, Twitter, YouTube and Snapchat. Now, online ads interrupt nearly everything.