Chart & Data Visualization Glossary
GLOSSARYThe vocabulary of charts, defined in plain English.
Every chart is built from the same handful of parts and ideas — an axis, a scale, a series of data points, a legend that names them. Once you know what those words mean, reading any chart (and spotting when one is misleading) becomes far easier. This glossary defines the core terms used across data visualization and statistics, with a concrete example for each and links to the related concepts and chart guides.
Browse the terms below. Each links to a short, focused page covering the definition, how the term shows up in a real chart, and how it connects to the rest of the vocabulary.
AxisA reference line that gives a chart's values position and meaning.
X-AxisThe horizontal axis, usually holding categories or time.
Y-AxisThe vertical axis, usually holding the measured value.
ScaleThe rule mapping data values to positions along an axis.
GridlinesFaint reference lines that help read values off a chart.
LegendA key that tells you what each colour or symbol represents.
Data SeriesA related set of data points drawn as one group.
Data PointA single value plotted on a chart.
TrendThe general direction a series moves over time.
MedianThe middle value of a sorted dataset.
QuartileA cut point dividing sorted data into four equal parts.
OutlierA data point that sits far from the rest.
Axis TitleThe label naming what an axis measures and its units.
Tick MarkA small marker along an axis indicating a value.
BaselineThe reference value, usually zero, bars are measured from.
Linear ScaleEqual distance means equal difference in value.
Log ScaleEqual distance means equal ratio, for huge ranges.
Categorical DataValues in distinct groups rather than on a continuum.
Continuous DataMeasurable numbers that fall anywhere on a continuum.
CorrelationHow two variables move together, from -1 to +1.
Regression LineThe best-fit straight line through scatter points.
PercentileThe value below which a given percentage of data falls.
RangeThe difference between the largest and smallest value.
VarianceThe average squared distance of values from the mean.
BinA value range in a histogram that data is grouped into.
Data LabelText on a chart stating a value exactly.
Box PlotA chart of the five-number summary of a dataset.
HeatmapA grid where colour encodes the value of each cell.