What is a Level 1 trading halt?

Excuse me, could you please clarify what exactly a Level 1 trading halt is? I've heard the term before but I'm not entirely sure of its specifics. Is it a temporary suspension of trading activities on a certain exchange or across multiple platforms? Does it apply to all assets or just specific ones? And what are the usual reasons behind implementing such a halt? I'd appreciate it if you could elaborate on the matter.