The perimeter of a wildland fire can always be split into different sections (i.e. head, flanks and back) according to their particular behaviour. The way to delimit the different sections of a fire perimeter depends firstly on the purpose and type of the analysis that is going to be carried out and secondly on the type of information available for that, but in summary we have observed that there is no bias-free and precise definition on the literature to delimit the head and the flanks of a fire perimeter which could be confidently used for scientific purposes. The aim of this paper was to explore a new definition to delimit the head fire perimeter that shall be objective, univocal, and adequate for scientific studies. Diverse options have been explored which have came out with five different criteria that can be used when analysing fire behaviour for scientific purposes. The use of one or other criteria will depend on the final aim of the study being undertaken.