To guess means to give an answer or form an opinion without having all the information you need to be certain. When your teacher asks how many jellybeans are in a jar, you make a guess based on the jar's size and your best estimate. When you're not sure if it will rain tomorrow, you might guess that it will because the sky looks cloudy.

A guess involves uncertainty. If you know the answer for sure, you're not guessing anymore. Sometimes people make educated guesses, using clues and reasoning to get closer to the right answer, like a detective piecing together evidence. Other times, guesses are pure shots in the dark, like guessing which cup hides the coin in a shell game.

The word can also mean to figure something out correctly, even without complete information: “How did you guess I was planning a surprise party?” In this sense, someone might be good at reading subtle hints or patterns.

Related expressions include “your guess is as good as mine” (meaning neither of us really knows) and “I guess so” (a somewhat uncertain agreement). Scientists form hypotheses and then test them, which is more careful than guessing, while wild guessing without any thought is sometimes called guesswork.