In an eventually consistent database, if you ask two different replicas the same question at the same time, you may get different answers. That is confusing! It would be a lot simpler if the database could give the illusion that there is just one replica. Then every client [ making a request ] would have the same view of the data and you wouldn’t have to worry about replication lag.
Designing Data-Intensive Applications – Martin Kleppmann
Consistency in the CAP theorem is actually Linearizability [ also called Strong Consistency, Atomic Consistency, External Consistency and Immediate Consistency ]. Linearizability is a recency guarantee i.e. the value read is the most recently updated in the database. In a linearizable system, as soon as one client successfully completes a write, all clients reading from the database must be able to see the value just written.
Computer Science 101