Michael Finkelstein, Eco-Woodturner

Ambrosia figure: or staining has streaks of color caused by an infestation of the ambrosia beetle. It creates a tapered,  
oblong shape running with the grain, and usually a grayish color.  Sometimes produces a  
“Starburst” Ambrosia figure. More photos

Bird's-Eye: : localized, small swirls of grain direction which look like a tiny eye. Please see photos of bark & wood to identify birdseye figure in a tree;              
 Sugar maple (hard maple)
bark with birdseye dimples and sugar maple' birdseye figure inside - cross-grain cut.
Field Identification of Birdeseye in Sugar Maple, by the USDA Forest Service USDA_research paper NC317 " also has lots of photos.

Blister or Quilted figure: closely crowded bulges or mounds elongated, creating an unusual 3-D effect

Broken-Stripe or Bee's Wing figure: ribbon figure in which the stripe effect is intermittent

Burls or Burrs: knob-like projections or bulges with swirling grain around clusters of buds, rings or eyes - formed along the tree trunk or limb

Chatoyancy: an optical reflectance effect that arises from the fibrous structure of a material or from fibrous  inclusions which give the effect of “cat’s eye” in   
minerals,  or a 3-dimensonial appearance in wood grain

Compression, Reaction or Tension wood:  caused by stress & appears as fine cross-wrinkles in  the grain usually caused by leaning of the bottom  tree
trunk into compression

Crotch figure:  where a juncture of the tree trunk develops an unusually twisted and inter-grown structure where two or more limbs merge

Curly figure: wavy or curly grain. Contortions in grain direction sometimes reflect light differently as one moves down the grain and this creates an
appearance of undulating waves known as
curly grain

Feather Crotch figure: a cut passing through the center of a crotch

Fiddleback figure: see Tiger-stripe

Flame maple:  also known as curly, fiddleback or tiger stripe, is a feature of maple in which the growth of the wood fibers is distorted in an undulating
chatoyant pattern, producing wavy lines.
Photos - flame figure in maple

Grain: describes the direction of the predominant longitudinal cells in a tree

Knots: are portions of a branch with irregularities inter-grown, over-grown or encased over a large branch

Mottled figure: occurs when the curly figure predominates in a piece with a combination of wavy and interlocked grain.

Pigment figure: distinctive patterns formed by uneven extractive deposits in the grain

Pommele figure: resembles a puddle surface, a dense pattern of small rings enveloping one another

Pith Flecks: bore holes from insects

Quilted figure: see blister

Ray Fleck figure: caused by ray structure that produces a series of shiny, light-reflecting surfaces which exhibit typical patterns  

Reaction wood: see compression.  Examples of Reaction wood

Ribbon or Stripe figure: vertical bands of varying luster and cell-vessel markings. Varied vessel lengths and light reflection create the pattern.

Spalted wood: wood with zone-lined decay. Spalting is any form of wood coloration caused by fungi. Although primarily found in dead trees, it can also
occur under stressed tree conditions or even in living trees. See
spalted wood photos

Swirl Crotch figure:  from the crotch area of the tree, the grain moves around in swirls.  A cut passing through the center of the crotch produces feather
crotch figure. if the cut is towards the outside of the crotch, a swirl crotch figure results.

Tension wood: see compression. Reaction wood forms when trees lean.  Compression wood forms on the lower side of the lean in conifers.  Tension
 wood is what forms on the upper side of the lean in woody angiosperms.  Tension wood is wood that is strengthened on the upper side of
 the lean or problem in hardwoods.  

Tiger-stripe: a cross-barred effect or “Fiddleback” figure. Also known as "flame" figure. Photos

Sources:  Wikipedia, Understanding Wood (ISBN 1-56158-358-8), Auburn University - Agriculture, Architecture Week Building Department, HobbitHouse
Inc.  and other  woodworking sites on the internet
Figure in wood is also known as "grain" and refers to the appearance of the side-grain cut

Figure results from a combination of anatomical features or the innate properties of the wood.
i.e growth structure and various abnormalities, plus orientation of the surface that results from the cutting process.

Simply put, internal and external stresses of various types ranging from lean forces to unfavorable climatic
conditions, disease, suppression, abnormal cell tissue and several other factors may contribute to
figure formation

The more uneven the grain = the more distinctive the figure
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