In Japanese, there are two sets of words we learn to describe various kinds of quadrilaterals.

**Mathematical terms** are 四角形【しかっけい】 *quadrilaterals*, 台形【だいけい】 *trapezoid*, 平行四辺形【へいこうしへんけい】  *parallelogram*, 菱形【ひしがた】 *rhombus*, 長方形【ちょうほうけい】 *rectangle* and 正方形【せいほうけい】 *square*. Some are specialized forms of others, as shown below:

[![enter image description here][1]][1]

If I remember correctly, Japanese people learn these terms in the 4th or 5th grade. Technically speaking, all 正方形 are also 台形, too. People say yes if someone asked "Is all 正方形 also 平行四辺形?" in math classes.

However, in reality, people usually use the most specific term when possible, and unspecific versions are used when they really need them. 菱形のハンカチ would normally refers to a diamond-shaped handkerchief even though a 正方形 is technically a 菱形, too. In most cases, this is not a *confusion* but an *optimization*; obviously, it's too bothersome to say 正方形ではない菱形の形をしたハンカチ or 角が90度ではない菱形のハンカチ in daily life. Likewise, when I hear someone say 長方形 in everyday situation, I usually assume it's an oblong rectangle.

That said, if I saw "the number of 長方形 is 2" in your example, I would still argue that it's technically incorrect, too, because they call it a *math textbook*! So it purely depends on the situation; the more the situation is closer to math, the stricter you should be.

There is also "easier" or "elementary" set of words suitable for kindergartners:

- 四角【しかく】
- 真四角【ましかく】
- 長四角【ながしかく】 or 細長い四角

Adults also use them in non-math situations. 四角 (without 形) [usually refers to squares][2] but sometimes includes rectangles. We should not be too strict on 四角, and we should not use these words if mathematical strictness is important. 真四角 specifically refers to squares, and 長四角 specifically refers to oblong rectangles like envelopes. After all, for kindergartners, people can easily avoid this problem by using ましかく and ながしかく.


  [1]: https://i.sstatic.net/tC2hA.png
  [2]: https://japanese.stackexchange.com/a/38517/5010