No, they're not the same thing. Nexus devices are devices marketed by Google, originally as developer devices, but now just as pure Google Experience devices. They can and have been made by a wide variety of hardware manufacturers, including Asus, Samsung, LG, and HTC.
Current phone: Nokia Lumia 520; Current tablet: Nexus 7 (2013)
Retired phones: HTC Dream, Nexus One, HTC One X (broken SIM slot ); Retired tablet: Amazon Kindle Fire (1st gen)