It’s a radio signal for a website, most commonly used for weblogs. More technically: “Rich Site Summary (RSS) is a lightweight XML format designed for sharing headlines and other Web content. Think of it as a distributable “What’s New” for your site.” See Intro to RSS for more info.
The Newspaper Association of America site has an informative article titled Syndication Made Simple. “Just as free e-mail newsletters enable publishers to directly reach readers and promote online and in-paper content, RSS “pushes” headlines and succinct, one-sentence article descriptions to those who subscribe to the no-cost feeds.”
The other side of syndication is aggregation. Here’s an article from Wired News that explains why aggregators are all the rage: Aggregators Attack Info Overload.
This icon is the cue that we’re RSS capable. So train your aggregator to grab content from the TTC syndicated weblog.