1, MM: it is a unit of length and also a unit of rainfall, abbreviated as mm in English. ?

2. centimeter: it is a unit of length measurement, equal to one hundredth of one meter.

3. Kilometers: Kilometers, also called kilometers, are units of length and are usually used to measure the distance between two places.

4. Addition: one of the four basic operations, which refers to the calculation of combining two or more numbers and quantities into one number and quantity. The addition symbol is the plus sign (+).

Math language is also difficult for beginners. How to make these words have more accurate meanings than everyday language also puzzles beginners. For example, the words "open" and "domain" have special meanings in mathematics.

Mathematical terms also include proper nouns such as embryo and integrability. But these special symbols and terms are used for a reason: mathematics needs accuracy more than everyday language. Mathematicians call this requirement for linguistic and logical accuracy "rigor".