Answer
"$a$ is divisible by $b$" means that when $a$ is divided by $b$, there is no remainder.
Work Step by Step
"$a$ is divisible by $b$" means that when $a$ is divided by $b$, there is no remainder (or the remainder is zero).
Example:
$48$ is divisible by $6$ since $48 \div 6 = 8$ with no remainder.
On the other hand,
$49$ is not divisible by $6$ since $49 \div 6=8$ with a remainder of $1$.
