http://docklandsljc.uk/2016/06/unicode-cuddly-application-se...
The BCD part is "binary coded decimal" - a way of representing numbers as decimal coded digits, so 0001 1000 meant "18".
The BCD Interchange code was a 6 but character set that allowed the standard encoding of uppercase letters and numbers. It was realised onto punched cards by utilising "digits" 11 and 12.
The extended binary decimal interchange code was a larger space (8-bit) that allowed the encoding of both uppercase and lower case letters.
Incidentally, the terms "upper case" and "lower case" come from printing presses where the individual letter punches (think the head of a typewriter) were stored in "cases" - actually a wooden storage drawer with lots of small rectangular components containing many of each letter; more for E and other vowels, less for Z and X - and since typesetting text involves more lower case than upper case (as per this post) the lower case letters were stored in the lower case so that they would be easier to reach, with the capitals being stored above and sightly further away.
That shipping deadline and the insane fallout from it has done more to keep me employed in my career than anything else.