In an EDI message the terminator character is used to allow the translator to recognise the end of the segment (or record). The delimiter characters are used to separate individual elements and sub-elements within the segment and, in effect, act as "terminators" for each piece of information.
for example:
Typically, in EDIFACT the ' (single quote) is used to designate the end of the segment, the + (plus sign) to separate the elements (including the 3 letter segment "tag" or identifier) and the : (colon) is used to separate sub-elements (elements which contain related pieces of information such as lines of an address).
In TRADACOMS the ' is again used to designate the end of the segment, the + to separate the elements the = (equals sign) to designate the 3 letter segment "tag" and the : is again used to separate sub-elements (elements which contain related pieces of information such as lines of an address).
Of course these characters can all be valid in any text field so they are usually escaped with the ? (question mark) when used in this way.
I hope this helps.
H.