It refers to importing various data (graphics, sound, etc.) from outside into a Unity project. The data to be imported has to be executable in Unity. Assets purchased from Unity Asset Store can be directly imported to Unity.
“Instance” refers to a copy which has entities created from Prefab. If you change the content of the Prefab, that change will also be reflected in the Instance. In the process of generating and arranging the same objects in large quantities, Prefab and Instance make it possible to collectively manage them, so it is one of the most important term in Unity.
*See the item of “Prefab”
“Isometric View” refers to display a scene by “isometric projection”. Unlike the Perspective View which has depth perception, the size of the object is displayed at the same proportions regardless of the distance.
* See the item of “Perspective View”