3D data acquisition is when we use special devices that take pictures and measurements of an object from different angles to create a 3D model of that object. Think of it like making a sculpture of a person, but instead of using clay, we use cameras and lasers to get really detailed information about the shape and size of the person.
Object reconstruction is when we take all of that information that we collected through 3D data acquisition and use it to create a digital 3D model of the object. It's like making a digital copy of the sculpture we made earlier.
To make it even simpler, imagine playing with your toy blocks. The blocks are like the pieces of information we get from 3D data acquisition. We collect these blocks from different angles and put them together to build a bigger structure, which is what we do when we reconstruct an object in 3D.