To add additional information to @jaypan’s answer following are my observations
node_field_data contains 6 fields
nid int(10) unsigned vid int(10) unsigned type varchar(32) The ID of the target entity. status tinyint(4) title varchar(255) uid int(10) unsigned The ID of the target entity. revision_translation_affected tinyint(4)NULL
the nid is primary key in this table and referred by node and other fields as target id.
The type attribute tells what kind of content it is referring to, like posts, article or custom. In case of custom, it will store the name of the content type.