Equation (noun)

1. A mathematical statement that shows the equality of two expressions by using an equals sign (=).
2. A formula or statement that describes a relationship between variables or values.
3. A balance or equality between two or more things or elements, especially forces or influences.

Origin:

From latin aequatio, meaning 'an equal division' or 'a state of being equal'.

Examples:

1. The equation 2x + 3 = 7 can be solved for x by subtracting 3 from both sides.
2. The equation of a line in two-dimensional space can be written in the form y = mx + b.
3. The equation of the state of a perfect gas relates its pressure, volume, and temperature.
4. The equation of love and trust is necessary for a successful relationship.
5. The equation of the budget must balance income and expenses in order to avoid debt.