Bond. Chemical Bond.

Might as well ride this puppy all the way to the end (of the week).

In chemistry, there are several ways that atoms can connect with each other to form molecules.

If two atoms each have one electron available (one that is not tightly bound to the nucleus) and one space empty which an electron can fill, a covalent bond can be formed.  In this bond, the atoms share their available electrons, so that each atom can be considered filled.  A simple example is the H₂ molecule. Each hydrogen atom has one electron, and can be filled when it reaches two (if you don't know why, don't ask; it gets complicated quickly). So by sharing electrons, each atom becomes stabler.

If, on the other hand, you have one atom with one more electron than it needs for a full set (say, for example, sodium) and one atom that is one electron short of a full set* (e.g. chlorine), the first atom can actually "give" the electron to the second, forming an ionic bond.

In a more complicated system, you might (for example) have a large number of atoms of a metal, many of which tend to be short one or more electrons.  When those atoms arrange themselves into a large structure (a block of metal as opposed to a single atom), the electrons have a tendency to un-attach themselves from their original atom and go wandering around, re-attaching themselves sporadically to other atoms.  Imagine a big parking garage, with cars pulling into and out of different parking spots but never actually leaving.  The forces that keep pulling the electrons temporarily down into different nuclei are what hold the whole megillah together.  This is called a metallic bond.

There are more bonds, of course, but they get progressively more complicated and obscure.  These are the ones you're most likely to encounter in Chem 101.

*"He's one electron short of a full orbital" is a favored insult in a certain circle of especially geeky chemists†.

†That circle being the one that exists in my head.