In the below code MAXERRORS argument defines the total number of records which can be rejected before entire file will be rejected by the system. It is a tolerant level and can be any integer number based on your discretion and requirement
ERRORFILE will define the name and path of the error log file which will contain the erroneous records rejected during Bulk Insert. It will contain maximum of MAXERRORS+1 records.
So in the above script complete file will be rejected only if more than 500 records are rejected during BULK INSERT and 501 records will be logged into Error log file which will be present at the path defined in ERRORFILE argument.
While if less than 500 records are rejected (or no records are rejected) than those records will be logged into error log file while rest of the records will be successfully loaded into the staging table.
Although these two arguments are rarely used but they can be very helpful if you want to know about the records which are rejected and also to set the tolerance level of the file loaded by defining MAXERRORS value.