save LAST_INSERT_ID to variable

I'm researching the LAST_INSERT_ID command for MYSQL.

from what i have seen - I can save it as a 'variable' as @variable =
LAST_INSERT_ID();

Question: What is the difference between @THIS_VARIABLE and
$that_variable (with a dollar $ sign)??

I cannot find ANY examples/tutorials that say we can save it as a  $variable.

-- 

Gordon.