Jail. The public areas of the iPhone or iPod to which, by default, Apple allows read/write access via USB. In Unix terms, this refers to the /private/var/root/Media folder.
Jailbreak. The iPhone and iPod touch hacks that allow users to gain access to the entire Unix filesystem. In Unix terms, this refers to changing the root of the directory tree to /.
Activation. The process that allows you to move beyond any of the various screens that instruct you to connect your device to iTunes before it can be used. On the iPhone, you can only make emergency calls until your iPhone is activated.
Bricking. To render an iPhone or iPod touch inoperable. The 1.1.1 firmware update turned many iPhones into iBricks. Users could not reactivate their iPhone to get past their "Please connect to iTunes" screens. Although the phones could still be used for emergency calls, users were locked out from all normal iPhone operations.
File system. The way your iPhone or iPod touch uses its memory to store data and applications. The iPhone and iPod touch use two "disks": a smaller private file system that contains the operating system and a larger public one that contains your media (songs, videos, etc), preferences, and data.
/etc/fstab. The file on your iPhone or iPod touch that states whether your file system allows read-write access.
SIM lock. A limitation imposed by the manufacturer of a GSM phone to limit a phone to certain carriers. The US iPhone is SIM locked and can only be used with AT&T.
Baseband. The part of an iPhone's memory that provides the firmware for the phone's radio modem chip.
GSM. Global System for Mobile Communications, a popular mobile phone standard used by the iPhone.
Unlock. Bypassing a phone's SIM lock to allow it to be used with any carrier with compatible equipment. In the US, the iPhone is compatible with both AT&T and T-Mobile's GSM equipment.
Unlocking Software. Software that allows the iPhone to be unlocked. You must jailbreak a phone in order to install and use unlocking software.
Third party apps. iPhone and iPod touch applications that were neither created by nor commissioned by Apple.
ssh. Secure shell. This is a shell that runs on your iPhone or iPod touch using port 22 and allows you to connect wirelessly to a Unix shell.
Toolchain. In terms of the iPhone/iPod touch world, a compiler and linker developed by Patrick Walton of the University of Chicago and his compatriots. It allows developers to create applications that can run on the iPhone and iPod touch's ARM processor.
DevWiki. The developer wiki for iPhone is hosted at iPhone.fiveforty.net. Many developer projects first appear here and the site contains a wealth of iPhone and iPod touch related information. The iPod touch Developer Wiki contains many of the most important recent developments regarding the touch. The phrase DevWiki may refer to either of these two sites.
Thanks Tony Hoyle, phire