HJKL are the movement key standard for NetHack. And also vi.
Contrast with WASD
Some programs (especially games) also provide keys for moving diagonally. Those usually are YUBN. They form a rectangle on US keyboards but are not as mnemonic on some international ones. And they get buggered to hell and back on a split (ergonomic) keyboard.
See also ReligiousWar
3 pages link to HJKL: