There's a couple of things happening here. Firstly, at the start, the * is the "universal selector", which targets all elements. The next bit qualifies it, though. It's an "attribute selector". It's targeting any element with a class that contains the string "col_". So the whole rule will target any element that has a class name that includes "col_".
So, for example, the rule would target all of these—
with the * looks for the "col_" string anywhere within the class name, whereas
targets any element whose class begins with "col_", and
targets an element with a class name ending with "col_".