[+]Modify [+]Copy [+]TransferFull Permissions. You can do anything you'd like with the object, script, or texture. Consider this setting for "learning tools".. and for freebies that are designed to be modified. Often used on freebies.
[-]Modify [+]Copy [+]TransferNo Mod. This setting is also used on freebies, particularly those who are afraid of wwhat a greifer might do with their object. This is also the setting used on many scripts. Allowing you to make use of the script, and copy the containing object, but not to muck around with the script. We call this "Safe but freely distributable"... think of it as "child proofing"
[+]Modify [-]Copy [+]TransferNo Copy. You can have only ONE of these things. It's precious on some level. a lot of higher priced items are set to this permission. Allowing you to tweak the model, change the colours, etc.. but not to have more than one of the item. + trans means that you CAN give it as a gift, or resell it if you can find a buyer. Amethyst collars use this setting. They can be resized, and given.. but can't be copied. Basically it keeps you from opening your own shop selling these items for cheaper than the other guy.
[+]Modify [+]Copy [-]TransferNo Transfer. You can make all the copies of this thing that you want, AND you can tweak it all out of shape.. but you can't give it to anyone else. This is a great setting for most clothes. Allowing the end user to change the sleeve length or tint as they desire, and copy it, and rename it into several different outfit folders... but they can't got into business selling your shirts.
[+]Modify [-]Copy [-]TransferMod Only. You can tweak this all you want, but there's only one, and you can't give it away. (allegedly this setting is impossible... but if subcontent (scripts for example) are no transfer, then the object becomes no transfer. A lot of premium poseballs and furniture have this setting.
[-]Modify [+]Copy [-]TransferCopy only. This setting is great for complicated, expensive items! (and the one I amd my partner use in our shop)... It's no mod.. so there's no chance of the end user mucking it up and coming back crying for a replacement.. it's copyable, so they can have multiple "instances" of the object in their inventory (backups)... but it's still no transfer, so their friends have to come back to us to get their own car.
[-]Modify [-]Copy [+]TransferTransfer only. I've never run into this setting in world, and can only think of ONE good reason for this setting.. works of art. With this setting, you can't modify it, you can't copy it.. but you can sell it or give it as a gift. Given SL's inventory glitches of late.. I really can't reccommend the use of this setting.
[-]Modify [-]Copy [-]TransferLocked up. Allegedly this setting is impossible, but it does APPEAR to happen when a no mod/no copy item contains some no-transfer content.. or vice versa. Basically this setting locks you down to an object you cant' change, can't copy, and can't sell it.