In F# what does the >> operator mean?

I noticed in some code in this sample that contained the >> operator:

let printTree =
  tree >> Seq.iter (Seq.fold (+) "" >> printfn "%s")

What does the >> operator mean/do?

EDIT:

Thanks very much, now it is much clearer. Here's my example I generated to get the hang of it:

open System
open System.IO

let read_lines path = File.ReadAllLines(path) |> Array.to_list

let trim line = (string line).Trim()
let to_upper line = (string line).ToUpper()

let new_list = [ for line in read_lines "myText.txt" -> line |> (trim >> to_upper) ]

printf "%A" new_list