Flashing ==> means installing a new ROM, Kernel or file.
ROM ==> is the operating system, any version of modded or un-modded android
Android ==> Google made operating system!!!
ODIN ==> Here, it means the program that you can use to flash ROMs (and other files) on your phone
ADB ==> A feature in android the allows the user to control the phone via commands
Soft brick ==> No, not the construction brick, this means you've got no working operating system or you have one but its damaged and you can't use it, so you cant see your homescreen, you only see a boot-loop when it wants to come up. You can view your recovery and boot loader (The download screen) when soft bricked, so you can easily fix this problem by re-flashing.
Hard brick ==> Similar to the construction brick, your phone with little hope of recovery without sending to the samsung base for repairs To avoid hard bricks, open the .TAR file which contains your ROM using winRAR, and check if it contains sbl.bin and boot.bin files or not
RIL==> Also known as a Radio Interface Layer. It is the communication layer between your phones modem and kernel.
What is a kernel?
Kernels are the software level of programming which allows the hardware and operating system to communicate properly. Kernels contain all of the devices drivers as well as some other information that allows the 'phone to be like a phone'. All operating systems have some sort of kernel, most are based on a linux kernel which have been modified to meet a specific use. In this case, android kernels are based on the linux kernel but has been optimized for mobile phones.
What is a custom kernel? What is the difference between stock and custom kernels?
A custom kernel is a kernel that has been made by a third-party developer (or someone else) and can have additional features such as overclocking support or undervolting support. The difference between stock and custom kernels are pretty much the same as what was mentioned before but stock kernels usually don't have support for overclocking and undervolting.
Modem (in terms of a phone modem)==> A modem, (sometimes referred to as a radio or baseband), is a driver that controls the sending and receiving of your mobile Network signals as well as switching between GPRS, 3G and HSDPA. It does not control Wi-Fi or the switchover between mobile signal and Wi-Fi. That is the job of the kernel. To locate your current modem details, go to... Settings > About phone > Baseband version.
Heimdall==> An application used to flash files for phones. It comes bundled with the command line tool and the app.
CWM==> Clockwordmod Recovery. Popular among almost all android ROM and kernel developers
TWRP ==> Team Win Recovery Project Recovery. Also popular among android ROM and kernel developers