Search channels provide a powerful way to search outside of FeedDemon's subscriptions. Simply select a feed search engine then enter your keyword, and FeedDemon will subscribe to a dynamic channel containing the search results for that keyword. This is a great way to find out when someone is talking about a topic of interest in a feed you're not already subscribed to.
A watch searches within the feeds you're subscribed to in FeedDemon, whereas a search channel enables searching all feeds that are indexed by a specific search engine.
