Something that is interactive is something that you can communicate or interact with. The coolest thing about the Internet is how interactive it is. You're constantly putting information and getting other information back.
Think of interactive as the adjectival version of the verb "to interact." The inter- part of the word means "between, together, among," while the act- part means "to do." Put them together, and you get "to do together or among." Turn that verb into an adjective, and you get interactive. Interactive games are the most fun, because the more you and the game interact, the more interesting it is.
