The most common and most likely answer to this crossword clue is the 7 plus 7 letter word BOOLEAN ALGEBRA
B
O
O
L
E
A
N
A
L
G
E
B
R
A
More clues leading to the result BOOLEAN ALGEBRA
Buddy explains!
The straight part
We know that "subject" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case subject = boolean algebra.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.