A partner introduction is the act of connecting with a partner-level investor at a venture firm rather than associates or analysts. The distinction matters because partners have actual investment authority and partner-level engagement is required for serious investment consideration, while associate engagement (though useful) doesn't drive decisions. The discipline is engineering partner-level introductions deliberately rather than accepting associate engagement as a substitute. Most rounds get decided by partners; partner introductions are the higher-leverage path.
The hierarchy:
Partners (general partners, managing directors): make investment decisions; lead deals; sit on boards.
Principals: senior investors, sometime...