The following documents the Pentaho Standards for Charting Terminology (pending review).
Since the images may be less-than-clear, the attached PDF document contains the same images in a more clear format.

Pentaho Charting Terminology Standards

Chart Categories

Charts will be broken into 2 categories for this description:

AXIS BASED CHARTS are charts that have one-or-more visible axis (examples: lines, bars, catigorical, etc.)
NON-AXIS BASED CHARTS do not have any visible axis (pie, polar, thermometer, etc.)

Since the above categories only differ in how the data is represented inside the plot area, there are a number of charting elements that are common to both chart categories:

CHART	The entire area being generated by the charting API.
PLOT	The area of the chart in which the data values are being represented.
TITLE	The main text used to name or describe the chart.
SUBTITLE	Subsequent text used to enhance the description of the chart.
LEGEND ITEM	A visual description of the mapping between a visual chart element and the business entity represented.
LEGEND	The area in which the LEGEND ITEM(s) are displayed
CHART BACKGROUND	The area of a chart upon which all other elements are placed.
PLOT BACKGROUND	The area of a plot upon which all other elements are placed.

NON-AXIS Based Charts

Inside the plot area of non-axis based charts, there are a number of elements:

EXPLODED	Any element of a chart that is slightly moved or exaggerated to show emphasis.
SECTION LABEL	The text inside the plot that indicates the name of a section

AXIS Based Charts

Axis based charts have two or more axis in the plot area used in the chart representation. Axis based charts have the following common elements inside and outside the plot area:

*Concept*	*Description*	*Alternate Names*
AXIS	A reference line (or ruler) upon which one dimension of the data is charted
RANGE AXIS	The ruler(s) against which the value dimension of the data is measured	Y Axis Value Axis
PRIMARY RANGE AXIS	The 1st or most-important range axis
SECONDARY RANGE AXES	All range axss that are not the primary range axis
DOMAIN AXIS	The ruler(s) against which the category dimension of the data is measured	X Axis Category Axis
PRIMARY DOMAIN AXIS	The 1st or most-important domain axis
SECONDARY DOMAIN AXES	All domain axes that are not the primary domain axis
AXIS TITLE	The descriptive text for an axis
ORIGIN	The intersection of the all the axes
MAJOR TICK	A mark on an axis at which a value is displayed and represented
MINOR TICK	A mark on an axis at which a value is implied but not displayed
TICK LABEL	The value displayed at a tick mark
GRID LINE	A line across the plot at a MAJOR TICK which helps visually indicate a value
ITEM LABEL	Text which indicates one value of the data at a specific data point on the chart
SCALE	The range of values represented on an axis
MAJOR INTERVAL	The value difference between major tick marks
MINOR INTERVAL	The value difference between minor tick marks
DATA POINT	One value being represented on a chart
DATA SERIES	A group of DATA POINTS all of which are represented the same way (bar, line, etc.)
ANNOTATION	A piece of information placed in the plot that indicates important information related to the charted data.	Target Line Band Line
BAR GAPS	The distance between bars of the same category on a bar category chart
CATEGORY GAPS	The distance between the last bar of one category and the first bar of the next category on a bar category chart
TRANSPARENCY	An amount (percentage) that indicates how much of the items beneath the specified item may be seen (100% = all, 0% = none)	Opacity (opposite) Alpha index
0 (ZERO) LINE	A line that indicates 0 (zero) on the Range Axis (not always at the origin)
3D	An indication that elements of the chart are rendered with a depth dimension