A notice of appeal is the document that starts a Tax Court of Canada appeal. It sets out the material facts, the issues, the statutory provisions relied on, the reasons the reassessment is said to be wrong, and the relief sought, and it must generally be filed within 90 days of the CRA's notice of confirmation (or after the 90-day no-decision threshold).
It is distinct from, and follows, the notice of objection: with very narrow exceptions, a taxpayer cannot file a valid notice of appeal without first having objected. In the Informal Procedure the document can be in plain language; in the General Procedure it is a formal pleading drafted to the Court's standards.