Definitions:

The least common multiple of two integers a and b is the smallest positive integer that is divisible by both a and b. It is usually denoted by

$$lcm (a, b)$$ If either a or b is 0, $$lcm (a, b) = 0$$

 A general example to help you recognize patterns and spot the information you're looking for

Number	Multiples of Each Number
3	3, 6, 9, 12, 15, 18, 21, 24, 27, 30
5	5, 10, 15, 20, 25, 30

The first common multiple of both 3 and 5 is 15.

In real life we use this concept when we try to plan how much items are going to be needed for events.