Plural of baseline: the back boundary lines in tennis courts, or more generally, any reference line or starting measurement from which changes are compared.
From baseline + -s (plural). Baseline itself comes from base + line, with the tennis sense emerging in the late 19th century.
Baselines are everywhere in modern life—in sports, business uses them to track if sales improved, doctors use them to see if treatment worked, making them one of the simplest but most important concepts in measuring progress.
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