Actually all three names describe the same process. I picked up this tintype at the flea market last summer. The tintype is a wet plate photographic process, in which a piece black enameled or varnished tin (in some cases iron) is coated in a liquid collodion to make an exposure. The image is technically a negative but because of the dark background it appears to be a positive. This technique for image making was first described in France in 1853 and patented in the United States in 1856, however with the development of the amateure camera it began fading in popularity by the end of the 19th century.
Further information on the tintype can be found on this web page.