Most comman Transfer type is a sheet of white vinyl with heat adhesive on the backside. The sheet is ran thru a digital printer to place your image onto the sheet. Once this is done it is ran threw a cutter that tracing the outter edge of the image with a blade. The user will pull of the outter material and place you cut out image onto the product and heat press it onto it.
A kiss cut vinyl transfer is taking a vector drawing and cutting the edges of it ( outter and inner ). In a solid color roll of vinyl. The user weeds out the cut material that is not part of the image/artwork and places the finish product onto the product. if multi colors are in need each color is cut seperate and placed and stack ontop of each other.
Both ways have its pros and cons.