Macro photography is close-up photography of small subjects, including things like bugs and flowers. You can take macro pictures in a studio or outdoor environment so long as you are magnifying your subject sufficiently.
Officially, you may hear that macro photography only happens when you take pictures of small subjects with a magnification of “life size” or greater. I will cover more about the meaning of magnification and life-size in a moment, but essentially it means that you must take pictures where your subject is the same size as your camera sensor or smaller, and it fills the frame. (So, if your camera sensor is one inch wide, you would be photographing something 1 inch or smaller.)
That is a very strict definition, and frequently you will hear photographers call an image “macro” even when it shows a slightly larger subject.