Database Design – What is Materialize?

When I learn the layout of the data, so I had a term Realize, which has no clear definition or explanation. So what is meterialize and what does materialize?

This question is not related to the materialized view and not speicalized with the specific DBMS.

The source that I learn: Youtube video of Prof. Dr. Jens Dittrich
: Mapping Relationships on Devices
At 9:24 we will have this term to materialize. He said that it was a process from the physical page to the storage devices.
And an additional question at this time: since the physical pages must also belong to the main memory, if we have a main momory database, so the data layout only exists in the main memory. Will there be materialize the process?