ODBC type "PG_TYPE_LO_NAME"

Under src/interfaces/odbc, connection.c generates the SQL statement

select oid from pg_type where typname = '" PG_TYPE_LO_NAME"';

and PG_TYPE_LO_NAME is 'lo'

lo does not seem to exist in pg_type.   How/where is it defined, and how is it
used?

Any tips on setting this up?

Thanks,

Matt