Newb Question, What is "gain advantage"

[FortunaPony]

Creating adventure for niece, not completely used to 5E anyways and the "Dawn of the 5th Age" says Unique Destiny ponies (Spiritual Path) "gain advantage on checks with a single skill or tool that is tied to the brand of destiny on your flank". What exactly is this advantage gained?

[David]

That is a 5th edition term for rolling twice and taking the better result.