Head up' is an expression that can be used to describe a variety of activities. The crossword solutions for the term 'head up' include 'RUN, ' 'LEAD, ' 'CLIMB, ' 'AVIATE, ' and 'goahead.' 'RUN' is an activity that involves moving quickly on foot, while 'LEAD' is a verb that means to guide or direct. 'CLIMB' is an action that involves ascending a vertical surface, such as a mountain or a ladder. 'AVIATE' is a verb that means to fly or operate an aircraft. Finally, 'goahead' is an expression that can be used to encourage someone to proceed with an action.