In a culinary context, turnover is a pastry-based food consisting of either a fully-enclosed (like a croissant) or semi-enclosed (like a sausage roll) filled pocket. Stewed fruit and/or jam are some possible contents for said pocket in the case of a sweet turnover, or meat and/or vegetables in savoury turnovers. Turnovers, also known as pasties or Cornish pasties in full, originated in Britain in the mid 1700s. They may be served hot or cold, and are a great easily-transportable food. There is a certain amount of controversy surrounding the "correct" size, shape and filling of turnovers, although the general idea is that the pastry is filled then "turned over".
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