Geometric Weird’s effect sets its power and toughness indefinitely until something sets them to a different number.

To determine its potential new power and toughness, count the number of spells and abilities that were on the stack at the same time, but don’t count abilities if you’ve already counted another ability from the same source.

Among abilities, only activated and triggered abilities use the stack. Activated abilities are written in the form “[Cost]: [Effect].” Triggered abilities use the word “when,” “whenever,” or “at.” They’re often written as “[Trigger condition], [effect].” Some keyword abilities are activated abilities and will have colons in their reminder texts, and some keyword abilities are triggered abilities and will have “when,” “whenever,” or “at” in their reminder text.