A technology transfer agreement is made between the shareholder and the startup, where the shareholder transfer (assigns, sells, conveys, etc.) specific intellectual property to the startup. A typical technology transfer agreement agreement will list the IP to be transferred to the startup, along with the shareholder representing he or she is the sole owner of the IP.
A technology transfer agreement is usually paired with a stock purchase agreement, as the IP transfer to the startup can be consideration (full or partial) for the shares purchased by the shareholder. Technology transfer agreements deal with IP that was created by the shareholder prior to being issued shares in the startup.