To gift a plot you must be the plot owner OR the mayor and the plot must be unowned. The player receiving the plot must be a resident of the same town. To gift a plot to another player the command is
/plot gift <player_name>
There is a fee of 25 gold and is paid by the person using the command. If the plot is owned by someone then the gold is paid by the character. If the plot is unowned it is paid by the town bank. This fee is paid to the game for safely transferring a plot to another person.
Example: /plot gift new_resident