LOW KEY
Source: 1.http://www.artistsnetwork.com/subject/other-subject/understanding-value-and-tone-for-better-painting
2.http://www.sensationalcolor.com/understanding-color/theory/high-key-low-key-color#.WgCyzROPKV4
3. Dictionary.com
Definition: “adjective, Also, low-keyed. 1. of reduced intensity; restrained; understated. 2. (of a photograph) having chiefly dark tones, usually with little tonal contrast (distinguished from high-key ).”
In my own words: Using dark tones with little contrast to another in one piece of work
Whistler used ‘low-key’ values 
HIGH KEY
Source:
1.http://www.artistsnetwork.com/subject/other-subject/understanding-value-and-tone-for-better-painting
2.http://www.sensationalcolor.com/understanding-color/theory/high-key-low-key-color#.WgCyzROPKV4
Definition: High key – (of a photograph) having chiefly light tones, usually with little tonal contrast (distinguished from low-key ). Origin of high-key.
In my own words: Using light hues/ tones with little contrast to another in one piece of work.
Monet used ‘high-key’ values and achieved dramatically different results.
NARROW RANGE
Source: http://www.artistsnetwork.com/subject/other-subject/understanding-value-and-tone-for-better-painting
Definition: “Today, many successful artists believe in keeping a narrow value scale – limiting their composition to approximately 4 values. In this case it seems, less is more and helps create a cohesive and harmonious work.”
In my own words: A small value scale with only about 4 values or hues
BROAD RANGE
Source: https://sites.google.com/a/stcc.edu/art103/home/assignments/color-variations
Definition: “Broad Range of Value: Many values (light to dark) present in an artwork.”
In my own words: Many hues or values present in a piece
TEXTURE DENSITY
Source: 1. www.wcs.k12.mi.us/cousino/wcsart/art%20foundatons%20site/texture.html
2. https://www.printingforless.com/printingglossary.html
Definition:
Texture: “refers to the surface quality in a work of art. … Some things feel just as they appear; this is called real or actual texture. Some things look like they are rough but are actually smooth. Texture that is created to look like something it is not, is called visual or implied texture.”
Density: “The degree of tone, weight of darkness or color within a photo or reproduction measured by a densitometer.”
In my own words: Creating texture by adding objects also in turn adds density
