What is the difference direct descendent (>) vs. descendant in jQuery selectors?

Have a look at jQuery Selectors

Child Selector ("parent > child") - Hierarchy Selects all direct child elements specified by "child" of elements specified by "parent".

Descendant Selector ("ancestor descendant")- Hierarchy Selects all elements that are descendants of a given ancestor.

$("#mainblock > div") = the childs only level

$("#mainblock div") = all the childs+ desendents.