A bucket brigade or human chain is a method for transporting items where items are passed from one stationary person to the next.
The method was important in firefighting before the advent of hand pumped fire engines, whereby firefighters would pass buckets to each other to extinguish a blaze. A famous example of this is the Union Fire Company. This technique is still common where using machines to move water, supplies, or other items would be impractical.
The method is applicable only if the number of participants is sufficient compared to the distance to cross.
Bucket Brigade as a Metaphor 
This principle inspired various technical items, e.g. the bucket-brigade device.
The term "bucket brigade" is also used for a certain method of organizing manual order picking in distribution centers. Here customer orders to be processed are passed from one order picker to the next. When the last picker in line has finished picking an order he walks back and takes over the work of the next-to-last picker, who in his turn also walks back and so on, until the first man in line is reached, who then commences picking an entirely a new order.
Similar applications of the idea of bucket brigades also exist for production lines.