In the context of the theatre, what are limes?

A dip into theatre history sometimes helps to explain many terms that originated in the theatre world and that have lived on in general English usage.

A good example is the type of stage lighting once used in theatres and music halls. An intense illumination is created when an oxyhydrogen flame is directed at a cylinder of calcium oxide also known as quicklime. Calcium oxide can be heated to 2,572 °C (4,662 °F) before melting. The light is produced by a combination of incandescence and candoluminescence. This effect was discovered in the 1820s by Goldsworthy Gurney (1793–1875). In 1825, a Scottish engineer, Thomas Drummond (1797–1840), saw a demonstration of the effect by Michael Faraday and realized that the light would be useful for surveying and other applications. The lighting came to be known as “Drummond light” (after the engineer) or “calcium light” (after the chemical element) or, in the theatrical world, as “limelight” (after the quicklime compound).

Although the technique has long since been replaced by electric lighting, the term “limelight” has nonetheless survived, as someone in the public eye is still said to be "in the limelight".

The lights that were used to create limelight in the theatre were called "limes", a term which was later transferred to the electric lights that replaced them.