A scuplture means that it is carved (verb, "to sculpt"). As the other members have mentioned, "statue" suggests that it is a human or animal form.

every statue is sculpture but not every sculpture is statue sculpture = anything carved of stone statue = human figure carved out of stone

To add to that, 'sculpture' can be used instead of 'statue' but 'statue' can't always be used instead of 'sculpture'. For example: 'What a lovely sculpture of a house!' - here it has to be sculpture as the house is neither animal nor human. 'What a lovely statue/sculpture of a dog' - here the dog is animal, so you can use either. If you can't depict what the object is, the best bet is to use sculpture :)