Email relay
When one person sends an email to another person, but they don't know the answer so they forward on to someone else they think is the right person to deal with the problem, that person in turn also doesn't know and once again forwards the email on to another person. This chain keeps on going until someone with the knowledge and expertise gets the forwarded email and eventually answers the question or sorts out the problem. All other people in the email chain are simply part of the relay of getting the baton (the email) to the last person who can cross over the finish line
The CEO Pierre sent an email to Antoine asking him for some figures for his work. Antoine doesn't have this information but thinks Gisele in Performance team might know and forwards this email on to her. Gisele also doesn't know but forwards the email onto Elena in Reporting team. Elena also doesn't know but forwards it on to Gary in Data Admin. Gary does in fact have a list of the figures Steve is requesting and so answers Pierre with the information required and thus finishing the email relay