When a big app says your stuff is “in the cloud,” that is a friendly picture of a very physical arrangement: buildings full of computers (often owned or leased by a handful of corporations), hundreds of miles away, running software that stores copies of your data on disks you will never touch.
Engineers joke that “the cloud is someone else’s computer.” More precisely: it is thousands of someone else’s computers, wired for power and cooling, with staff who replace failed drives at 3 a.m. Your notes, chats, and uploads become files or database pages on those machines — replicated for durability, scanned by automated systems, and governed by a company’s policies and the laws where they operate.
Custody is the question: who holds the authoritative copy, and under whose rules? If the canonical copy lives only in a vendor’s tenant, they are the custodian — you have access through an account, not possession of the bits.
Providers replicate data across drives and regions; backups may lag; legal holds can override your UI. None of that is unique to one bad actor — it is how large-scale storage works. Understanding that helps you judge what “I own my data” can mean on someone else’s farm.