Hols means holidays: days off school or work, or a trip away. It is a short British word, informal and a little school-like. A child in Britain might ask, “What are you doing in the hols?” Americans almost never say this; they say vacation, or holidays. You would not put hols in a serious letter. It is simply holidays with the end cut off. Though actually, to some ears it can sit uncomfortably close to holes (gaps), which is a completely different word.