There are two kinds of Application Commands: global commands and guild commands. Global commands are available for every guild that adds your app; guild commands are specific to the guild you specify when making them. Command names are unique per application within each scope (global and guild). That means:

• Your app cannot have two global commands with the same name
• Your app cannot have two guild commands within the same name on the same guild
• Your app can have a global and guild command with the same name
• Multiple apps can have commands with the same names

Global commands are cached for 1 hour. That means that new global commands will fan out slowly across all guilds, and will be guaranteed to be updated in an hour. Guild commands update instantly. We recommend you use guild commands for quick testing, and global commands when they're ready for public use.