The Holly Poly Exchange

Altered Carbon nominator. The shortest way to explain it is that in the series, personhood (personality/memories) is stored as data, so a person can wear different bodies over the course of their lifetime. It's also possible for a person to be using more than one body at a time. Takeshi Kovacs wears different bodies over the course of the series, and also spends some time "double-sleeved" (in two different bodies). Let me know if more clarification would help.