This is the 273rd most frequent Russian word.
произошло
"Happened" or "occurred."
Here, 'произошло' is used to inquire about a past event or occurrence, asking for clarification or details.
Что произошло вчера во время встречи?
What happened yesterday during the meeting?
In this sentence, 'произошли' (plural form of 'произошло') refers to specific events (the changes) that took place.
Все изменения, которые произошли за последний год, стали неожиданными.
All the changes that occurred over the past year were unexpected.
Here, 'произошло' emphasizes the occurrence of a single unexpected and extraordinary event.