DEC is the decimal format of the talkgroup. It's a number used in trunked systems to identify the talkgroup. You'd program this into your scanner and treat it as a channel so to speak.
HEX is the hexidecimal value of the same number. Some scanners/radios use hex instead of dec. It just makes it easier so you don't have to convert to one or the other.
Mode depicts whether it is digital or analog.
Display is what is displayed on the radios display. It's usually limited to less than 16 characters, so it just an abbreviation of the actual description, i.e., "SHERIFF DISP".
Description tells what the talkgroup is used for, i.e., "Sheriff's Dispatch".
