Answer:
Valence electrons are the electrons in the outer-most shell of of the atom. They are typically the electrons which are involved in forming bonds to other atoms (as opposed to the other so-called "core" electrons which do not interact much with other atoms or molecules.
See the Related Questions links below for more information and for how to count the valence electrons of an atom.
Any electrons located in the outer shell of an atom are known as valence electrons.