In the context of the numbers presented, 10, 4, and 6 represent terms that could relate to various mathematical operations. The number 4 in this particular scenario is referred to as the subtrahend if we consider that it is being subtracted from 10 to reach 6. In a subtraction equation like 10 – 4 = 6, the number from which another number is subtracted is called the minuend, which is 10 in this case, while the number being subtracted (in this case, 4) is the subtrahend.
Therefore, to answer your question, the correct term for the number 4 when used in this context is subtrahend.