A FIFO lane (First In, First Out) helps manage flow in a process. It is exactly what it sounds like. The first item coming into a process is the first one worked on.
FIFO lanes provide consistency and predictability. They create a link between a process and its upstream supplier.
A FIFO lane
Can limit WIP. Some FIFO lanes limit the amount of work that can pile up, preventing overloading a downstream process.
Prevents working out of sequence. This is especially important in office environments where cherry-picking (selecting easy work first) can disrupt flow.
Can be a pull signal. When a FIFO lane has an open space, it is a signal to send more work.
On the shop floor, FIFO lanes are often conveyors or roller tables. In the office, it can be something as simple as a series of numbered folders that contain work documents. The quantity of these folders limits the work in the queue. If an empty folder is available, it is filled with work, and placed at the back of the queue.