what is should

The word "should" is a modal auxiliary verb used to indicate what is proper, reasonable, or the best thing to do. It is often used to give advice, make recommendations, express obligation, talk about probability or expectation, and show conditional mood. For example, "You should get some rest" suggests that resting is the best option. "Should" is followed by the base form of the main verb and does not change form for different subjects. It can also express a past obligation or regret when combined with "have" and a past participle, as in "I should have studied".