Is any number except letters, including positive and negative integers and positive and negative decimals, fractions, zeros and irrational numbers (such as π). For example, the ratio of the circumference to the diameter of a circle is π, and the expansion coefficient of iron is 0.0000 12.
Constant is a name with a certain meaning, which is used to replace numbers or strings, and its value never changes. In mathematics, the capital letter "c" is usually used to represent a constant. A mathematical constant refers to a constant with a constant value, and vice versa. Unlike most physical constants, the definition of mathematical constants has nothing to do with all physical measurements.
Extended data
For example:
In the polynomial 6X-2X+7, 6X, -2X and 7 are its terms, where 7 is a constant term;
In polynomial x? +2x+ 18, whose term is x? 2x and 18, where 18 is a constant term;
In polynomial 5x? -3x+4，5x？ , -3x, 4 is its term and 4 is its constant term.
More specifically, 0 is also a constant term, but 0 has no degree.
Another thing to note is that π and e are not letters, but constant terms. For example, the coefficient of πab is not 1, but π. Because π represents a specific number: 3. 14 15926...π is also a constant term. e = 2.7 1828 1828459 ......