Geometry – Key Terms & Definitions
Essential geometry vocabulary for IGCSE Mathematics (0580). Each term includes a clear definition and example to help you understand and remember key concepts.
angle
CoreAmount of turn between two lines
Example
Measured in degrees
parallel
CoreLines that never meet
Example
Same direction, equal distance apart
perpendicular
CoreLines meeting at 90°
Example
Height perpendicular to base
polygon
CoreClosed shape with straight sides
Example
Triangle, square, pentagon
regular polygon
CoreAll sides and angles equal
Example
Equilateral triangle, square
congruent
CoreExactly the same shape and size
Example
SSS, SAS, ASA, RHS tests
similar
CoreSame shape but different size
Example
Corresponding angles equal
circle theorem
ExtendedRule about angles in circles
Example
tangent line
ExtendedLine touching circle at one point
Example
Perpendicular to radius at that point
chord
CoreLine segment with both ends on circle
Example
Diameter is longest chord
arc
CorePart of circle circumference
Example
Major arc is the longer part
sector
CoreRegion bounded by two radii and arc
Example
Like a pizza slice
segment
ExtendedRegion between chord and arc
Example
Minor and major segments
symmetry
CoreShape looks same after transformation
Example
Line symmetry or rotational
bisector
CoreLine cutting something in half
Example
Perpendicular bisector of a line
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How many geometry terms do I need to know for IGCSE?
This glossary covers 15 key geometry terms. Focus on understanding definitions and being able to use each term in context during exams.
Are these terms for Core or Extended?
Terms are labelled as Core or Extended. Core students should focus on Core-labelled terms, while Extended students need to know all terms.
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