Perspective shows the relationship between objects in a photo as seen by the viewer. For example, closer objects might appear much bigger. Farther away objects might appear smaller. Straight lines may appear to come together in the distance.
Perspective can also relate to where the camera is relative to the subject. For example, you might take a photo from above the subject or you might take it lying on the ground looking up at something.
These are examples of pictures using perspective.

Credit: Flickr user fklv

Credit: Jan Arendtsz
More on perspective in photography:
- “How to Use Perspective in Photography Effectively” from Skylum
- “Perspective in Photography: Tips for Beautiful Photos” from Lightroom Presets