A proband is an individual serving as the starting point for the genetic study of a family (used especially in medicine). A proband is usually the first affected individual in a family who brings a genetic disorder to the attention of the medical community.
A trio refers to 2 parents + 1 offspring (2 + 1 = 3, hence trio). In medical genetics, trio analysis often means the analysis of a proband's genome and along with their parents genome. An exome trio-based approach is fundamental to the identification of heterozygous dominant pathogenic variants (in an afflicted proband and their unaffected parents).