What does it mean when someone is board?

When someone writes that a person is "board," they have almost certainly made a common typographical error intended to spell "bored," which describes an emotional and psychological state of apathy, listlessness, and mental fatigue caused by a lack of engaging activities, interesting stimuli, or meaningful mental stimulation. In this state, individuals often feel that time is passing extremely slowly and actively seek out entertainment, hobbies, or social interactions to remedy the monotony. However, if the spelling is intentional and refers to the physical noun "board," it might metaphorically describe someone as being stiff, rigid, or uncompromising in their posture or demeanor, behaving somewhat like a wooden plank, though this is a very rare and non-standard figurative usage compared to the ubiquitous typo.

Assuming you mean when someone is "bored": When someone is bored, it means they are feeling mentally listless, uninspired, weary, or restless because their current environment, task, or conversation fails to capture their attention. Their lack of stimulation can make time feel like it is passing very slowly, prompting them to seek out entertainment, distraction, or a change of pace. If someone accidentally types "board" instead of "bored" in a text message, it carries this exact same psychological meaning. You can verify this definition by checking standard English dictionary entries for emotional states.