When a PL/pgSQL function is called as a trigger, several special variables are created automatically in the top-level block. They are:

NEW

Data type RECORD; variable holding the new database row for INSERT/UPDATE operations in row-level triggers. This variable is NULL in statement-level triggers.
OLD

Data type RECORD; variable holding the old database row for UPDATE/DELETE operations in row-level triggers. This variable is NULL in statement-level triggers.
TG_NAME

Data type name; variable that contains the name of the trigger actually fired.
TG_WHEN

Data type text; a string of either BEFORE or AFTER depending on the trigger's definition.
TG_LEVEL

Data type text; a string of either ROW or STATEMENT depending on the trigger's definition.
TG_OP

Data type text; a string of INSERT, UPDATE, or DELETE telling for which operation the trigger was fired.
TG_RELID

Data type oid; the object ID of the table that caused the trigger invocation.
TG_RELNAME

Data type name; the name of the table that caused the trigger invocation.
TG_NARGS

Data type integer; the number of arguments given to the trigger procedure in the CREATE TRIGGER statement.
TG_ARGV[]

Data type array of text; the arguments from the CREATE TRIGGER statement. The index counts from 0. Invalid indices (less than 0 or greater than or equal to tg_nargs) result in a null value.