Is there any sigificance of the Alpha, Beta Theta, etc. categories?
What do the SL, AR, LT, etc. call outs stand for?
How does the Beta AR compare to the Theta AR?

Here's some more information in addition to Benjamin's contributions. * Sigma-- Softshell(mostly Gore Windstopper fabric) * Gamma -- Softshell (mostly Polartech Power shield fabric) * Delta -- Insulation (Mid layer) pieces * Alpha -- Goretex hardshell * Beta -- Goretex hardshell (climbing) Cut shorter, with 2 hand pockets * Theta -- Goretex hardshell (Skiing inspired, usally 3 layer Gore) longer cut, powder skirt, waist draw cord and extra chest pockets. * Rho-- Base layers ( synthetic and merino) * SV --Severe-- Heavier (tougher) fabric , larger (helmet compatible) hoods * AR--All Around-- usally slightly lighter then SV and more all around features * LT -- Light-- Lightweight ,usally XCR ,fewer features * SL-- superlight--Super Lightweight, lightest fabric, minimal pockets or vents * SK--Ski-- only SK item is the Theta SK pants, Great heavy duty bib ski pants * MX--Mixed-- Gamma MX series only, Polartech power shield * Comp--Composite-- Combination of hardshell and softshell

Here you go: * Alpha: Technical focussed high-end items * Theta: All Around oriented * Beta: Trimmed down, minimalist * Fission: Primaloft Insulated * Gamma: Softshell * Switchback: Ultralight Softshell * Sigma: Windstopper * Delta: Midweight Insulation - Fleece-like * Rho: Base Layers * Gothic: Wool Abbreviations * SV=Severe * AR=All Around * LT=Lightweight * SL=Superlight * SK=Ski/board specific * MX=Mixed Use