Welcome to the forum, Lou
. The section on the left of thr chart that encompasses culverins is more a generic for guns basic typology. In fact, and as you may see in the 'class' column, culverins and half culverins are long barreled pieces with a significant reach. Also you may see in the chart that a (legit) culverin is over four times heavier than a falcon.
As per the term, culverin in English, Colubrina in Spanish and Portuguese and Couleuvrine in French, derive from the Latin term for Cobra (snake). As you well know, in an early stage artillery pieces were given animal names.