In 4D 2004, triggers execute one at a time (except for the On Load Record event) for all tables.
In 4D v11 SQL, triggers execute in parallel per table. That is, for any given table, triggers are still serial but the triggers for different tables can be executing in parallel.
This can be very dangerous if the triggers are sharing resources (for example interprocess variables or a plug-in) and the developer assumes that triggers are fully serial and does not do anything to protect the shared resources (e.g. using semaphores).