Odd-one-out (mathematics vocabulary) Which word does NOT belong with the others? Choose the single best answer.

Introduction / Context:
This vocabulary-based odd-one-out distinguishes geometry terms from an algebraic concept. Four options are squarely within elementary geometry, while one belongs to algebraic notation and general mathematics rather than shapes or measures in plane geometry.

Given Data / Assumptions:

• Options: area, variable, circumference, quadrilateral, perimeter
• Assume standard school-level definitions.
• Exactly one term should not be a geometric attribute or shape name.

Concept / Approach:
Identify which options name geometric quantities or figures. 'Area,' 'circumference,' and 'perimeter' are measures associated with shapes; 'quadrilateral' is a class of four-sided polygon. 'Variable' denotes a symbol representing a quantity, typically used in algebraic expressions, not a geometric measure or figure.

Step-by-Step Solution:

Verification / Alternative check:
Attempt to pair each term with a formula specific to geometry. You can write formulas for area, circumference, perimeter, and properties of quadrilaterals. While variables appear in those formulas, the term 'variable' itself is not a geometry-specific quantity or shape, confirming it as the outlier.

Why Other Options Are Wrong:

• Area: fundamental geometric measure.
• Circumference: specific to circles.
• Perimeter: measure around polygons.
• Quadrilateral: class of plane figures.

Common Pitfalls:
Noting that 'variable' is used in geometry formulas and thinking it belongs. The question asks which does not belong by domain specificity. 'Variable' is general-purpose and does not denote a geometric measure or figure by itself.

Final Answer:
variable