What is the '

Example:

sentence = <<~ LOTSOFWORDSthis is an example of the thing initialising a variable, how else does this work?LOTSOFWORDS

I don't think it's the shovel operator, there's no tilde in that. I'm doing a Kata that forms string variables with it, so that much I know.

I have tried looking on Google for '<<~', 'less than less than tilde' and a few other guesses at what it's called. Any clues so I can work it out?