休憩 きゅうけい : break at work (昼休み is actually a type of きゅうけい) OR break from studying/training. Just long enough to eat some food and stretch - usually 15 minutes to an hour.

休み やすみ: a day off from school or work.

休日:きゅうじつ; A holiday - Christmas, Arbor Day, etc.

休暇:きゅうか: long vacation from work (maternity leave, 2-week vacation to Barbados, etc.)