Where is the transform.position inside of a GameObject?

I’m new to unity and game development but I’ve been thinking about this problem. I don’t know where the transform.position of a gameobject really is and the documentation kind of skips that detail. If I create a new cube, is the transform.position smack dab in the center or the object or is it in the center at the bottom or something else completely?

Isn’t knowing the position of the transform essential to finding the sides of the mesh? For example, the x of the right side of a cube would always be transform.position.x + 5 in a 10x10x10 cube if the transform.position is exactly in the center. But, it’s transform.position.x + 10 if the transform is in the upper left corner so I feel like knowing the transform.position is really important.

How else can I attach prefabs together? I want to build walls without gaps between them.

The transform.position is wherever the pivot point of the mesh is.