The Pas d’Arms was a very specific format for medieval deeds of arms. It always involved a specified number of defenders agreeing to meet all comers on terms specified in advance. It sometimes, although not always, included considerable ceremony.
For those who currently recreate medieval deeds of arms, “Pas” is often used as a shorthand description of any recreation of medieval deeds that attempts to come closer to medieval models than the standard double elimination tournament of the SCA, that places less emphasis on objective competition, and that involves considerable ceremony.
This is not what a Pas was in the Middle Ages. It was only one format among many: other formats, for example, arranged both comers and defenders in advance. The rules of a Pas could be designed to yield an objective winner to a highly competitive contest, and sometimes ceremony and speeches were clearly less important than a briskly arranged series of combats.