It behaves similarly to the other associated functions, here's a quick overview of what they return.
Originally Posted by AnthonySterling
reset - First value in array
end - Last value in array
each - Array containing key/value pair (twice) for current item
current - Current value
key - Current key
next - Next value in array
prev - Previous value in array
They will return FALSE if the function cannot get what it wants (e.g. reset() with an empty array, prev() when at the beginning of an array, etc.).