A 'fresh law' (my term) issue occurs when a party tries to raise new legal issues on review (appeal or judicial review) for the first time - ie. that they did not already raise at the trial/hearing level.
It's very similar to the recognized trial/hearing principle that a party may not appeal on the basis of evidence being admitted where they did not 'object' to the disputed evidence admission at trial. It's also the legal corollary of 'fresh evidence', which is a well-known issue of appeal (and now judicial review) law. "Fresh evidence" is about trying to admit new evidence at the appeal stage when, for whatever reason, the party didn't get it in the trial or hearing stage.