A terminating decimal has digits that end. They do not go on forever. For example, 0.125 has only 3 decimal digits and does not keep on going like 1/3
A rational number is a number that canbe expressed as p/q where p and q are both integers. But q cannot equal to 0.
All terminating decimals are rational numbers, but not all rational numbers are terminating decimals. For example 1/4, which equals to 0.25 is both a rational number and a terminating decimal. On the other hand, 1/3 is a rational number but is not a terminating decimal.