¯ — Negative

Literal. Keys: Alt-Minus

¯ belongs to the number, including exponents and complex components. - is a function.

¯2+5               ⍝ 3
1E¯3               ⍝ 0.001
2j¯3               ⍝ 2j¯3
¯1r2               ⍝ ¯1r2

Numbers covers how numbers are written.