PeopleSoft stores object definitions types such as Record, Field and SQL definitions as numbers in PeopleTools meta-tables. Here is a list of what each number means with respect to its definition.

Definitions for Record Object Types

The following are stored on the PSRECDEFN table on RECTYPE field.
RECTYPE = 0
Corresponds to: SQL Table
Comments: The record will be built as an actuall database table.

RECTYPE = 1
Corresponds to: SQL View
Comments: The record will be built as an actuall database view.

RECTYPE = 2
Corresponds to: Derived/Work Record
Comments: This type of record provides a working storage in the component. This is NOT a database object.

RECTYPE = 3
Corresponds to: SubRecord
Comments: SubRecords are used to group fields together or other subrecords. Subrecords are added to records and they are not database objects.

RECTYPE = 5
Corresponds to: Dynamic View
Comments: Does not correspond to a database object. A dynamic view is an SQL executed by PeopleTools.

Definitions for Field Object Types

The following are stored on PSDBFIELD table on the FIELDTYPE field.
FIELDTYPE = 0
Data Type: Character

FIELDTYPE = 1
Data Type: Long Character

FIELDTYPE = 2
Data Type: Number

FIELDTYPE = 3
Data Type: Signed Number

FIELDTYPE = 4
Data Type: Date

FIELDTYPE = 5
Data Type: Time

FIELDTYPE = 6
Data Type: Date Time

FIELDTYPE = 8
Data Type: Image

FIELDTYPE = 9
Data Type: Image Refrence

Definitions for SQL Object Types

The following are stored on PSSQLDEFN on SQLTYPE field.
SQLTYPE = 0
Data Type: Stand alone SQL objects

SQLTYPE = 1
Data Type: Application engine step

SQLTYPE = 2
Data Type: SQL belongs to a view

SQLTYPE = 5
Data Type: These are querries for DDDAUDIT and SYSAUDIT (very interesting SQLs)

SQLTYPE = 6
Data Type: Application engine XML definition.

Pages, components, menus and other PeopleSoft objects are also stored as numbers in PSPROJECTITEM table (stores PeopleTools project objects). Check this post for a list of object types.
I think this covers it all, let me know if I've missed something!