In a Concept Network, the activation value of a node is normalized (for example between 0 and 100) and shows the "activity" of the node.
When the activation value is high, one can think that the node has been used, activated, or was near to another node, that was itself activated (in this case, activation was propagated to it. One could say that the node is a part of the current "thoughts" of the system.
When this value is low, one can think either that it has been recently deactivated (because of a great decay rate, or because of an agent action), or that is has not recently been activated.
One could say that the node is a part of thoughts that are away from the focus of the system.