An exhibition is a collection of items for public display, like an exhibition of children’s artwork, antique vases, or memorabilia from a science fiction movie series.
In the 19th century, exhibition was used to refer to a collection of objects, while exhibit designated a single item in an exhibition. Nowadays, exhibition and exhibit are often used interchangeably. Exhibition comes from the Latin ex-, meaning "out," and habere, meaning "hold" — as objects in an exhibition are "held out," or shown, to the public. The h in "hold out" might help you remember to include the h when spelling exhibition.