Darksteel Ingot. Indestructible is a static ability that means that any permanent that has indestructible cannot be destroyed, and cannot be destroyed as a result of lethal damage.
The less-than symbol (<) represents an inequality in which the number or problem on the left is smaller than that on the right; however, it can be reversed (>) to show that the item on the left is greater than that on the right.
The less-than symbol, as well as the greater-than symbol, can be used for more than just showing which number is larger than another. In fact, many inequalities require you to solve the problems on each side of the less-than symbol in order to determine the relative value of a variable.