Meaning

noun conveyance consisting of a wheeled support on which a camera can be mounted

noun conveyance consisting of a wheeled platform for moving heavy objects

noun a small replica of a person; used as a toy

originFrom doll + -y, from the given name Dorothy, originally applied either to a woman or female pet or to a children's toy, and expanded to refer to various types of contrivances or devices. The Online Etymology Dictionary, while considering the reason for applying it to such devices unobvious, compares how the names jack, jenny and jimmy are also applied to devices.

Etymology from Wiktionary, CC BY-SA 3.0