What does range 2 ... -1 mean? (Ruby koans about_arrays.rb)

Please can someone explain what a range object means 2..-1.

Ruby koans has the following meaning in about_arrays.rb:

def test_slicing_with_ranges
  array = [:peanut, :butter, :and, :jelly]

  assert_equal [:peanut, :butter, :and], array[0..2]
  assert_equal [:peanut, :butter], array[0...2]
  assert_equal [:and, :jelly], array[2..-1]
end

The following website (found in another answer) explains how to work with cutting ranges: Gary Wright, fragments of strings / arrays From this I understand why the split gives the answer, which he does. The thing I don't understand is WHAT, which the range object belongs to. For the normal range, I can do:

(1..3).each { |x| puts(x) }

which gives the following output when executed in irb:

1
2
3
=> 1..3e

However, (2..-1).each { |x| puts(x) }it gives:

=> 2..-1

So what does range mean (2..-1)?