Octothorpe — Definition, Formula & Examples
Octothorpe is the formal name for the # symbol, commonly called the number sign, pound sign, or hash mark. In math contexts, it is placed before a numeral to mean 'number,' as in #5 for 'number five.'
The octothorpe (written #) is a typographic symbol consisting of two horizontal and two vertical strokes that intersect to form a grid pattern. In mathematical and general notation, it serves primarily as an abbreviation for the word 'number' when placed before a digit or as a label marker in enumerated lists and data sets.
How It Works
When you see # before a numeral, read it as 'number.' For instance, #12 means 'number 12,' often used to label items in a list or identify a specific data point. In some programming and spreadsheet contexts, # can signal an error code or a comment line, but in standard math class, its role is simply as a shorthand label. Do not confuse it with any mathematical operation — the octothorpe does not indicate addition, multiplication, or any arithmetic.
Example
Problem: A teacher labels five test scores as #1 through #5. Score #1 is 88, Score #2 is 92, Score #3 is 75, Score #4 is 90, and Score #5 is 85. What is the value of Score #3?
Step 1: Identify what the # symbol means here. Each #n is a label for 'number n' in the list.
Step 2: Look up the score corresponding to label #3.
Answer: Score #3 is 75.
Why It Matters
You will encounter the # symbol when labeling data points, reading survey results, or referencing items in a numbered list. Knowing its proper name and meaning prevents confusion when reading math problems, spreadsheets, or standardized test instructions.
Common Mistakes
Mistake: Thinking # represents a mathematical operation like addition or multiplication.
Correction: The octothorpe is only a label meaning 'number.' It does not perform any calculation. If you see #7, it simply means 'number 7,' not 'do something to 7.'