Colon (:) in test datasets

Hey guys, not a data scientist here, but a software engineer. Getting started with learning some AI for a side project, and after doing some reading on AI as a service on Amazon web services, I got linked in an article over to here. There is one thing I don’t understand, and I know this is a dumb question, but what does the colon mean in the test data sets? For instance in

0 1:1 9:1 19:1 21:1 24:1 34:1 36:1 39:1 42:1 53:1 56:1 65:1 69:1 77:1 86:1 88:1 92:1 95:1 102:1 106:1 117:1 122:1

Thank you.

Take a look at https://xgboost.readthedocs.io/en/latest/tutorials/input_format.html