Isolations are the idea of moving a part of your body separate from another. We do this all the time say moving one leg in a step while the other is supporting your weight off the ground (Isolating your legs). In dance we name isolations when we are doing mechanics that are creating this isolation outside of every day motions.
For example:
Moving one hips in the opposite direction as the shoulders
Moving the head without moving the rest of the body
Lifting One Shoulder
In partner dance there are two primary forms of isolation:
Partner Isolation These move differing body parts in opposition to each other. This means for every motion there is a counter motion both of which are detectable to the partner allowing the partner to match the isolation by feeling the opposition.
Solo Isolation These move a part of the body while keeping the rest still in relation to a fixed point. This creates a showy isolation to an audience but hides the isolation from a partner connected to the stationary part. This means your partner wont feel the isolation and thus the initiation. Followers will need to struggle to catch up using vision.
Isolations are inherently more confusing than a whole body motion as the follower needs to understand both the initiation direction(s) as well as map the disparity. This means when communicating isolations intended for both parties they are usually emphasized especially in the dimension most connected to the partner.
Isolations which do not do this tend to get uncertainty stillness or a small fraction of the motion that the leader is doing.
If the leader is initiating a isolation they do not want the follower to do it is important to communicate something to the partner even if it is just Validation that they are where they need to be.
Isolations that are intended for the follower only are best communicated by a matching motion in the connection that express larger in the followers body be it due to Impetus Leads or perpetual momentum principles. This involves Grounding the leader’s movement that would otherwise create a matching isolation.