When you search for a pattern in Vim, it’s stored to the / register. This then can be used to store the query in some variable for some Vim command, or perhaps paste the pattern as text. For example, the following invocation in normal mode:

"/p

pastes the search pattern in the current buffer. This same register value is used for repeat searches (n in normal mode). I’m not sure when I’m ever going to use this, but at least I’ll start to understand some shortcut on vim.fandom.com or SO that has an odd / in the command.