In the field of cell biology, TNF-related apoptosis-inducing ligand (TRAIL), is a protein functioning as a ligand that induces the process of cell death called apoptosis.

A trail is usually a path, track or unpaved lane or road, though the term is also applied, in North America, to routes along rivers, and sometimes to highways. In the United Kingdom and the Republic of Ireland path or footpath is the preferred term for a walking trail. Some trails are single use and can only be used for walking, cycling, horse riding, snow shoeing, cross-country skiing, etc., others, as in the case of a bridleway in the UK, are multi-use, and can be used by walkers, cyclists and equestrians.