Systems where teams of people or devices take turns carrying out a task, or electrical switches that respond to current changes. In sports, races where team members run successive portions of the total distance.
From Old French 'relais' meaning fresh horses stationed for couriers, from 'relaier' meaning to leave behind. The electrical sense developed in the 19th century from the concept of passing signals along.
The Pony Express used relay stations every 10-15 miles, allowing mail to cross the continent in just 10 days when it previously took months. Modern internet communications use a similar relay principle, with data packets hopping from server to server across the globe in milliseconds.
Complete word intelligence in one call. Free tier — 50 lookups/day.