Hey there!
The LCM between two numbers is (unabbreviated) the Least Common Multiple, or the first shared number they have in common when self-added.
For example;
5 & 7.
5 = 5, 10, 15, 20, 25, 30, 35.
7 = 7, 14, 21, 28, 35.
The Least Common Multiple (LCM) is 35.
Now, let's do our numbers.
8 = 8, 16, 24, 32, 40
10 = 10, 20, 30, 40.
The Least Common Multiple (LCM) of 8 &10 is 40.
I hope this helps!