A mesocyclone and a tornado are related weather phenomena, but they are not the same thing. A mesocyclone is a rotating updraft found within a thunderstorm. It can be thought of as a large-scale feature that can lead to the formation of tornadoes under the right conditions.
In contrast, a tornado is a smaller, more intense column of rotating air that extends from the base of a thunderstorm to the ground. Tornadoes usually form from mesocyclones when the conditions are conducive for their development.
To summarize, a mesocyclone is the parent circulation that can produce tornadoes, while a tornado is a specific and dangerous manifestation of that rotation that touches the ground.