Resolution is a term used to describe the quality of a digital photo or video image, camera sensor, video display screen or projector. 

The quality is usually broken down into the number of pixels it's capable of generating or displaying.

The higher the number of pixels, the better the quality on the whole, though this is also proportional to the size of the image, sensor or screen.

When is comes to the camera, setting the image resolution is integral to producing the quality you want. 

Video resolution is the image size measured in pixels, Image Length X Image Height

For video images, pixels are dots of light, which composed, form the picture. They can be square or non-square (rectangle, used in anamorphic filming)

Resolution choices should be determined by the intended outcome, such as the method of presentation, social media, large screen, etc. but also may be affected by the recording device restrictions related to time & space.

-              If you are aiming to produce footage intended for a short film, promotion, online presence, show reels, etc, use the highest quality HD setting available, and that your computer and editing software is capable of processing and storing. If in doubt always do a test prior to a shoot.

-              If you are filming for general documentation, for long duration performances, or with minimal post processing or storage capabilities available, resolution may be lowered accordingly. 

Examples of some well known standard resolutions:

Resolution is one indicator of quality, but overall video quality has a number of additional factors which include Sensor Type, Sensor Size, Sensor Resolution, Codecs, Data Rate, Colour Science, Dynamic Range, etc. 

In other words not all 1080 footage will be the same. 

Cameras will often indicate either a bit-rate (mbps) or may simply indicate High Quality / Standard Quality, etc. 

See the recording settings of your individual camera for the quality options for each resolution.