Define octet rule.

Explanation

**Step-by-Step Solution:**

1. **Definition of the Octet Rule**: The octet rule is a principle in chemistry that states that atoms tend to combine in such a way that they each have eight electrons in their valence shell, achieving a stable electronic configuration similar to that of noble gases.

2. **Atoms Combining**: Atoms can combine with each other to form compounds or molecules. This combination can occur through two main processes: the transfer of electrons (ionic bonding) or the sharing of electrons (covalent bonding).

3. **Achieving Stability**: By either transferring or sharing electrons, atoms aim to complete their outermost shell with eight electrons. This completion of the outer shell is what we refer to as achieving an "octet."

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