Okay little one, imagine you are part of a big group of friends, like a class at school. Now, within that group, there might be some smaller groups or cliques that are really close and they hang out together more often. These smaller groups also have a leader or a person who is the most important in making decisions for the group.
In mathematics, there is something called a group too, which is a bunch of elements that have a special way of combining to form other elements. Now, within a group, there might also be some smaller groups or subgroups that are really important and have a leader or a special person. The Frattini subgroup is one such subgroup.
The Frattini subgroup of a group is the intersection of all of the normal subgroups (like those smaller groups within your class) that contain all of the so-called "non-generators" of the group. "Non-generators" are the elements of the group that can't be used to make all of the other elements through combination.
So, in simpler terms, the Frattini subgroup is like the smallest subgroup that contains all the important people or elements that can't be replaced by others in the group. It helps mathematicians understand how a group is built and organized, just like how cliques help you understand the dynamics of your class.