There is a zone where a camera can only focus its lens at a single point, but there will be an area that stretches in front of and behind this focus point that still appears sharp. This zone is called the depth of field. The depth of field is not a fixed distance because it can change in size. It described as either shallow when only a narrow zone appears sharp. It can also be described as deep when more of the picture appears sharp.
To be able to control the depth of field you need to know how to control your aperture first. You need to know how much depth you want in your picture. If you’re taking a portrait. it’s better to have a shallow depth of field so that the focus is on the person’s face. Having a shallow depth is also good when you need to separate a subject from a busy background, street shooting, event shooting, and many other things! On the other hand, when taking landscape photos, you want to make sure you have a deep depth of field so that everything in the frame is in focus.