This one is much less brainy and more feely, and I think overall more useful. But it is also a concept that is deployed ubiquitously in Latin/Rhythm/Smooth, but almost never in Standard, because it is easiest by far to study and utilize in hand-hold positions. As a result, the other three styles have a body of theory and language for the idea, but Standard mostly doesn't. Let's see how well it translates!
(ETA: Having said that, I was first introduced to this idea eight years ago in a private lesson with no less than Charlotte Jorgensen, Standardite extraordinaire. I simply was not well-equipped at the time to understand. The Smoothies and Latineers that visited the concept with me later had a much simpler context & language for showing & telling me.)
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The base context here is that the dancers' connection always has some baseline force (pressure or tension, 3-5 out of 10 in intensity, dancers' preference). Critically, it is also both parties' responsibility to maintain that baseline. So if the leader changes the force in the connection, the follower should respond in a way that equalizes back to baseline.
For example. In a pressure connection, if the force increases, the follower steps backward to reduce it. If the pressure reduces, they step forward to increase it. By contrast, under tension, an increase of force invites the follower to step forward and a reduction invites them to step backward.
That principle works fine for beginners and maybe intermediates, but all too soon another layer is needed. It turns out there are two different ways that the leader can change the force in the connection, and correspondingly two ways that the follower is expected to respond.
That difference hinges on whether the leader moves the connection point or not as they change force. Force changes in a moving connection invite movement, equalizing back to baseline; but force changes in an UNMOVING connection invite the follower to add reciprocal force, aka charging the connection.
For example. In a pressure connection, the leader can increase the connection force. If they do so while moving the connection point, this invites the follower to step backward, just as above. But if they do so without moving the connection, this invites the follower to compress into them, preparing some sort of explosion movement.
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If you follow this logic a little way, you'll notice that it is impossible for the follower to instantaneously detect if the connection point is moving or not. The sensation of pressure change will always come before the sensation of movement.
Therefore, the follower's initial reaction to a change of force in the connection should be to resist rather than equalize, as though this were a static line, and then change their response once they detect that the connection is in fact moving. This principle, applied skillfully, is the base cause of gooey elasticity in open Smooth positions as well as the snappiness of Latin & Rhythm actions.
But it turns out that principle also applies to Standard as well, with the same benefits--it is just that there are many fewer configurations of connection! To wit, there is a distinction between charging and moving, and a highly sophisticated couple will pass through a brief charging phase at the start of most movements.
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How does this apply to Promenade opening in International Tango specifically? Simply that the couple charges the connection more than they do at other moments or in other dances. This charge slightly delays the final release, and adds some visible snap to it.
In other words, the response is immediate, but initially resistive. It changes character after a certain threshold of telegraphed intent. Much easier felt than explained, I'm afraid!