parsimony
Explanation
The Joke
A serious-looking man wearing glasses and a suit sits at a bar and orders "Occam's Cocktail." The caption below the panel simply reads: "A scientist orders whiskey."
The joke is that "Occam's Cocktail" -- named after Occam's Razor, the principle that the simplest explanation is usually the correct one -- would logically be the simplest possible drink. A cocktail typically involves multiple ingredients mixed together, but the most parsimonious version of a cocktail would strip away all unnecessary components (mixers, garnishes, bitters, ice) until you are left with the simplest possible drink: just straight whiskey.
The Humor
The humor is dry and minimalist, which is fitting for a joke about parsimony. The comic itself embodies the principle it references -- it is a single panel with minimal dialogue, and the caption is as stripped-down as the drink being ordered. There is also a layer of character comedy: the man is so committed to the principle of parsimony that he applies it even to ordering drinks at a bar, which is both admirably consistent and absurdly pedantic. The title "parsimony" reinforces the theme.
References
Occam's Razor (also spelled Ockham's Razor) is a problem-solving principle attributed to the 14th-century English friar William of Ockham. It states that among competing hypotheses, the one with the fewest assumptions should be selected -- often paraphrased as "the simplest explanation is usually the best." The principle of parsimony is foundational in scientific reasoning and is used across disciplines from physics to biology to philosophy.