What the asterisk means in math
Most of the time, * means multiply: 6*7 is 42. That comes from computers, where * is on every keyboard and × isn't. In advanced math, * has several other jobs, from convolution to complex conjugates.
Multiplication
Programming languages, spreadsheets, calculators and search engines use * for multiplication because early computer keyboards had no × key. So 3*4 means 3 × 4. In handwritten or typeset math, use × or a centred dot · instead. * looks like a typo there.
A related convention: in Python, JavaScript and several other languages, ** means "to the power of", so 2**3 is 8. Our guide to the asterisk in code covers the other jobs * does in programming.
Other meanings in mathematics
| Notation | Meaning | Field |
|---|---|---|
| f ∗ g | Convolution of two functions | Analysis, signal processing |
| z* | Complex conjugate of z | Physics and engineering (mathematicians usually write z̄) |
| A* | Conjugate transpose of a matrix | Linear algebra |
| V* | Dual space of V | Linear algebra |
| Σ* | All strings over an alphabet (Kleene star) | Computer science, regular expressions |
Which asterisk character to use
For typeset math, use the asterisk operator ∗ (U+2217, \ast in LaTeX). It sits on the math axis, level with + and =. The keyboard * sits higher and looks out of place in a formula. For a superscript star like z*, LaTeX's z^* gives the right result.
The circled asterisk ⊛ and squared asterisk ⧆ are separate operators with their own meanings in specialist fields.