What is the meaning of the number of terms?

All u need to understand is what is terms
terms could be a number or a unknow number (ie. x, y)
so for example:
Consider the number of terms in the sequence 1,3,5,7,9,11,13,... , and
consider the number of terms in the sequence 2,4,6,8,10,12,14,.... They
have the same number of terms, because we can match them up one-to-one like
1 3 5 7 9 11 13 15 ...
2 4 6 8 10 12 14 16 ...

If we add the first sequence and the second sequence we still have the same no of term
ie.
1 3 5 7 9 11 13 15 ...
2 4 6 8 10 12 14 16 ...
1 2 3 4 5 6 7 8 ...