What is the := operator?

In some programming languages, I see (ex.):

x := y

What is this := operator generally called and what does it do?

In all languages that support an operator := it means assignment.

• In languages that support an operator :=, the = operator usually means an equality comparison.
• In languages where = means assignment, == is typically used for equality comparison.

does := mean =?

I can't recall any languages where := means the same as =.

In MySQL := and = are both used for assignment, however they are not interchangeable and selecting the correct one depends on the context. To make matters more confusing the = operator is also used for comparison. The interpretation of = as either assignment or comparison also depends on context.