Anticathexis is a kind of repression. If and when the id ascribes some psychic energy to an image or a potential action that is unhealthy, detrimental, or socially unacceptable (according to the judgment of the ego), that image/action will be blocked or "binded" by the ego. This process of blocking or censoring is anticathexis.
Cathexis itself is when a person invests psychic energy in an idea or thing. This is often defined as an impulse, desire, drive, etc. When this investment is taboo or deemed unhelpful by the ego, it is blocked or transferred into something else. Sometimes the ego will perform a double anticathexis: i. e. blocking the id's irrational fear of giant spiders and blocking the superego's feeling of embarrassment for having such a fear.
When the psychic energy of cathexis is diverted, during the process of anticathexis, it often is turned (by the ego) into an opposite. For example, unconscious (or id-derived) fear of giant spiders might be transferred to a conscious courage with very small spiders. This is a compensation (or over-compensation); an indirect way of dealing with the fear.
Based on Freud, it was suggested that psychic energy or biological drives are continuously being generated by this energy and only a certain amount is available at a given time. This energy is therefore transmitted to the ID, Ego, or superego where this energy is transformed. Without going into great detail about the ID, Ego, and superego, remember that the ID does not decipher between reality and fantasy, so because of this it can act in unrealistic manners or ways that may not be socially acceptable to some. In a sense, the Id and the Ego work to balance each other out and make the ego makes sure that the ID is acting or being "socially acceptable" or being seen as acceptable. Kind of like a lifeguard who watches the pool for acceptable and unacceptable behaviors in order to prevent future occurrences. Cathexis is an investment of energy in an idea, thought, object, or person. The ego is able to capture some of this energy that the ID gives off and use it to its advantage as well as make sure it is appropriate and socially acceptable. The ego does this best by using repression which is by pushing these thoughts out of mental awareness and keeping it "behind the scenes, so to say" and making sure the ID is acting in an appropriate manner. By repressing these thoughts the ID may or may not have, the ego is "blocking" unwanted or unacceptable behavior by pushing it farther back into the unconscious thought process, but this takes an enormous amount of energy and will at once resurface if an action triggers it.
In psychoanalysis, anticathexis, or countercathexis, is the energy used by the ego to bind the primitive impulses of the Id