When defining a file layout it is placed in the file section of the data division. Each record begins with an "01", a space, and the record name. Fields within a record traditionally began with 05?

The question describes COBOL's hierarchical data structure. Level 01 defines a record. Level 05 fields within that record can be further broken down into subordinate fields (level 10, 15, etc.). The 10-level field described in the question is indeed a breakdown/subfield of the 05-level field, showing the nested hierarchy of data definitions.