Hypotheses is the plural of 'hypothesis' — a guess or possible explanation for something, made before you have enough proof, which you then test to see if it's true. Scientists form hypotheses and then run experiments to check them. You'll usually see this word in science, research, or careful, formal writing — in daily talk, people are more likely to just say 'guesses' or 'ideas.'

假設（複數，hypothesis的複數形）