What was the PlayStation 3's system software interface called?

The PlayStation 3’s system software interface was called the XrossMediaBar.

The XrossMediaBar, commonly abbreviated XMB, organized the PlayStation 3’s functions along horizontal categories with selectable items arranged vertically. Users could access games, videos, music, photos, settings, and network features through the interface.

Sony also used the XMB on other products, including the PlayStation Portable and some Bravia televisions. Its cross-shaped navigation design became strongly associated with Sony’s mid-2000s consumer electronics.

XrossMediaBar is the interface name, not the name of Sony’s online service. PlayStation Network provided online accounts and services, while XMB was the menu system used to navigate the console itself.