To help you defien the two let's use wikipedia:
Wikipedia says" A
marketplace is the space, actual,
http://wiki.answers.com/wiki/Virtual_(computing) or metaphorical, in which a
http://wiki.answers.com/wiki/Market operates. " In application the market place is a generic reference to peopel that might buy that product or service.
Wikipedia says "A
target market is a group of customers that the
http://wiki.answers.com/wiki/Business has decided to aim its
http://wiki.answers.com/wiki/Marketing efforts and ultimately its
http://wiki.answers.com/wiki/Merchandise." In application a Target Market is more specific to your business. For example, Kim's Pizza may target college students opposed to Bill's pizza that targets football lovers.