The Vietnamese word "lú" is an adjective that describes someone who is a bit slow in understanding things, or someone who is not very sharp or clever. It can be translated to English as "dull-witted" or "foolish." It is often used to describe a person who might seem confused or unable to grasp concepts quickly.
"Lú" is a versatile word that can describe someone who is not quick-witted or who might be confused. Use it in a casual context, and remember that it can have a teasing tone.