Shimmer – subtle (usually metallic) color mixed very evenly in base color (typical color balance has more pigment than shimmer, but there are also sheer shimmers )
Micro-shimmer – very fine metallic/sparkly particles mixed evenly throughout base color (this finish is often smooth to the touch)
Micro-glitter – fine metallic/sparkly particles suspended in base color (this finish may feel a little rough to the touch, but not always)
Glitter – chunky and more visible glitter particles suspended in base color (this finish usually feels rough to the touch)
Frost – icy/frosty finish with a predominant metallic look (typical color balance has more frost than pigment)
Lustre – pearly finish – can be pearl/white, gold, silver or iridescent – not as predominant a finish as a frost, sometimes light-reflecting
Creme – no shimmer – a milky, creamy finish that can be sheer or opaque
Jelly - like a creme, there is no shimmer. Jelly-like in texture and very often sheer, with an extremely glossy finish (OPI is trying to now refer to this as Sorbet)
Prismatic micro-glitter or shimmer – fine rainbow colored particles that flash multi-colors & reflect light, some have a holographic or “3D” quality. (Also referred to as Holographic/Holo)
Iridescent – usually gives a color a “flash” of another color, depending on how light is reflected on the surface. Opalescent is similar, although typically has a distinct ‘pearly’ quality
Matte/Suede – satin or flat looking polish. No gloss or shine
Duo-chrome – a shimmer polish that appears as two or more shades, depending on the light
There's also a great tutorial over at Lacquerized, which includes pictures and definitions and hits about every possible type of polish you might ever encounter. It's awesome!
My definitions above are mostly cribbed from Suze and All Lacquered Up.