It's a way of writing strings without having to escape things or having line breaks mess things up (a heredoc, if you're familiar with that terminology). For in

It's a way of writing strings without having to escape things or having line breaks mess things up (a heredoc, if you're familiar with that terminology). For instance, <<-END this is some text END will give you a string containing " this is some text\n". END can be anything. It's particularly useful in metaprogramming, since you can maintain formatting, and you don't have to escape " or ' if they happen to show up in your code. What's interesting in the OP's example is that you end up passing three strings " text of one\n", " text of two\n", " text of three\n". I had no idea that would happen, though I have seen things like define_method <<-RUBY, __FILE__, __LINE__ + 1 some_code RUBY so it makes sense. Ruby treats anything on the same line after the comma as separate arguments, so even though __FILE__ comes after <<-RUBY and before RUBY, it really appears after the final RUBY to the interpreter.