To ‘Pig Out’ means to eat ravenously; gorge oneself. The phrase describes a situation where you ate a lot more than you should have.
Example of use: “Last night I watched such a sad movie, I pigged out on a full carton of ice-cream to make myself feel better.”
In comparison with many other statements, the origin of the idiom “pig out” is quite new – it was first used in 1979. Because pigs have voracious appetites, it is not surprising that they gained a reputation for gluttony; the comparison between human eaters to pigs have been common throughout history. While some idioms are hard to relate to, “pig out” is one that makes sense.