interactive

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Acting or capable of acting on each other.
• adjective Computers Of or relating to a program that responds to user activity.
• adjective Of, relating to, or being a form of television entertainment in which the signal activates electronic apparatus in the viewer's home or the viewer uses the apparatus to affect events on the screen, or both.

from The Century Dictionary.

• Mutually active; acting upon or influencing each other.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Acting with each other.
• adjective computer science Responding to the user.
• noun A feature (as in a museum) that can be interacted with.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective capable of acting on or influencing each other
• adjective used especially of drugs or muscles that work together so the total effect is greater than the sum of the two (or more)