Unrigged: Unrigged meshes are static pieces that don’t bend or move with your body. They can be moved and resized like normal prims.
Examples: Lips (Loud Mouth, Soul Kissers, etc) Lady bits (Coochie and SKING) and older mesh breasts (Lolas Tango) are often Unrigged.
Rigged: Rigged meshes move with your body, bending and contorting as you move. Their shape can be adjusted slightly with a select number of sliders, but otherwise their appearance is fixed and they cannot be resized.
Examples: Older Mesh Legs (Phat Azz) and most Mesh Heads.
Fitmesh: Fitmesh is actually a type of Rigged Mesh. Fitmesh greatly improved the ability to adjust a meshes size and shape. Almost all your shape sliders will effect the appearance of a mesh that is Fitmesh. The degree to which it is effected varies greatly, but overall, the customization options are much greater then with normal Rigged mesh. The major exception to this is face sliders, which were left out of the Fitmesh Update. While there’s a small number of head sliders that can be used, for the most part “Fitmesh heads” behave like Rigged heads. What you see on the AD is all you get.
Examples: Maitreya, Belleza, Tonic, Slink and almost every other ‘Modern ‘Mesh Body on the Market.
Bento: Like Fitmesh is a Type of Rigged Mesh, Bento is actually a type of Fitmesh! Bento is taking the improvements Fitmesh made and taking them further, adding additional attachment points and sliders for Mesh Makers to attach to. Bento items are able to utilize many more of the face sliders as well as take advantage of new bones in the fingers to create Heads that are fully customizable and fingers that move independently of one another. The first Omega Friendly head with Bento, LightStar, has hit the market and we expect hands to hit soon after. After that, new bones have been added for tails and wings, so who knows what lovely things will end up in our laps?
Examples: LightStar + ?