The symbol for "approximately" resembles a normal equals sign, but the lines are wavy instead of straight. One wavy line instead of two stands for a weak approximation.
This sign is regularly used in mathematics to show that an answer is not exact, such as rounded decimals. For example, pi is approximately equal to 3.14 and uses this symbol to denote that there are many other digits in pi that aren't listed.
A related symbol is "not equal to," which means the answer is not the number listed. This symbol is a regular equals symbol with a diagonal line dividing it in half.