Space-time Human Internal Fluctuating Transfer, abbreviated to "SHIFT", is a phenomenon that occurs in certain individuals in the Zero Escape franchise. Put simply, those with this innate ability are able to transfer their consciousness across space-time when they find themselves experiencing a life-threatening crisis. This includes to alternative histories, as well as the past and the future, by any measure between a few hours, to decades. However, the target location they jump to has to have a version of their own body for their consciousness to enter, that is alive. Therefore they cannot jump to a history or time period where they do not exist, or are not alive.
Those with this ability are a variation of "espers". Within the context of Zero Escape, espers are those who have a strong resonance to the joint morphogenetic field. The ability works by swapping two different consciousness at two points in space-time; The "SHIFTer's" consciousness leaps into the target body, which forces the consciousness that already resides in it to be forced out and into the body the SHIFTer left behind. Since the swap typically occurs because the SHIFTer is seconds away from death, his means that in order to SHIFT, the SHIFTer must effectively kill their alternative selves. This raises the issue of morality surrounding the ability, which became the subject of debate when the group in Zero Time Dilemma had to decide whether it was right to swap their consciousness with completely innocent versions of themselves to save themselves.
Depending on how powerful of an esper you are, depends on how much control you have over SHIFT. Those who first awaken to it often develop "Reverie Syndrome", in which their brains effectively go on stand-by due to not being able to cope with what it's experiencing. The memories of SHIFTing don't stay at first, and memories of alternative histories simply seem like vivid dreams, or bizarre out of body experiences. When someone with the ability who can't remember their SHIFTs subconsciously recalls information they aren't supposed to know, it comes across like they experienced a sudden influx of thoughts that don't align with their own memories. Once someone begins to gain more control over their jumps, they are able to recall them, however the memories are often still foggy. When a group of SHIFTers SHIFT together, the resonance makes their abilities stronger, and the memories are easier to retain.
Although life-threatening danger is required to SHIFT, the especially power esper Akane Kurashiki has been shown on an occasion to be able to initiate a SHIFT without any such danger being present. Although she was extremely emotionally devastated at the time, which suggests that certain espers may be able to iniate their abilities from experiencing other negative feelings besides danger.