infinite
Explanation
In this comic, a student approaches a professor and asks about infinity: "Can you explain the infinite?" The professor explains that you have to distinguish "potential infinite from actual infinite" -- you can count as high as you want, but that's just a potentially infinite process, not an actual infinity. There's a meaningful way to talk about infinity, but it's not just about counting numbers.
The student is initially engaged but then becomes agitated: "But in serious stuff in calculus things work because the infinite is there." The professor responds "Right, no way around it" -- and in the final panel, the student is shown panicking: "What in the hell? I am freaking out man, I am freaking out!" while the professor sits calmly next to a "Calculus Professor" sign.
The humor captures the genuine existential vertigo that many math students experience when they first seriously engage with the concept of infinity. The distinction between potential and actual infinity is a real and important one in mathematics and philosophy (going back to Aristotle), and the realization that actual infinities are unavoidable in calculus (through limits, infinite series, etc.) really does unsettle people who think deeply about it. The joke is that this profound mathematical crisis is presented as a casual office-hours conversation, with the professor completely unfazed while the student has a full breakdown -- reflecting how mathematicians have long since made their peace with infinity while newcomers find it deeply unsettling.