The following concepts are explained in depth in the earlier Data Model lesson. To recap, a Keyspace is a collection of tables with attributes that define how data is replicated across nodes (Replication Strategy). It defines a number of options that apply to all the tables it contains. It is generally recommended to use one Keyspace per application, and thus a cluster may define only one Keyspace.
A Table is how Scylla stores data and can be thought of as a set of rows and columns.