What's Daisy Chain? What's Function?

Let's see below pictures to have a more clear idea.

Daisy Chain Function

Space saving and keep grow tent tidy, more convenient and safer in use.

How many? Usually 2-5 lights can be chained in a line,depends on the different modes. Some low wattage grow lights can have 10 max to be chained.

What line used?

The line is the same line of power cable.