What is a harpsichord? where were these instruments often found?

A harpsichord is a keyboard instrument with strings that are horizontal and run upright on the keyboard in a long, narrow case and are plucked by points of quill, leather, or plastic operated by distressing the keys. They were often found in European classical music of the 16th to 18th centuries. 

Answerthe third and fourth;

It should be classical period