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.