Operators that compare two values and return a true or false (or boolean) value based on their relation to one another. They are also sometimes called comparison operators. For instance, "10 > 5" means the number 10 is greater than 5, assuming we use the decimal number system (my personal favorite). It would return a true value because it is true. Different programming languages and notations use different symbols, but here are some common ones.
= or == means "is equal to"
> means "is greater than"
< means "is less than"
>= means "is greater than or equal to"
<= means "is less than or equal to"
<> or != means "is not equal to"
These are the notations that I know. /msg me or write up ones from other systems if you like.
You should also check the documentation for the language you are using, because some relational operators do not return a truly boolean value but an integer. For instance, one of Java's primitive data types is boolean, but in C, relational operators return an integer. Some languages have these operators return 0 and 1, others 0 and -1. Understanding the return value of relational operators is very, very important.