The term you refer to where anime or manga characters tend to look less detailed is super-deformed, which appears in spin-offs of popular anime or manga, an example being "Naruto Spin-off: Rock Lee and his Ninja Pals," and is also used humorously to show confusion, tiredness, unusual excitement, and more.
According to https://tvtropes.org:
An artistic style in anime in which a normally (more) realistically proportioned character is rendered in a shorter, rounder form, often with a big head and short limbs, somewhat resembling a caricature of themselves as a tiny yet plump toddler.
As previously stated, this "super-deformed" art style can be used in many ways, and is also known as chibi. You did indeed state that you do not think this art-style is known as chibi, but it actually is..
Chibi is a Japanese slang word describing something short. The term is widely used to describe a specific style of caricature where characters are drawn in an exaggerated way: small and chubby, with stubby limbs and oversized heads.
This certain description is seen in the image you have posted. Such related description is also shown in the image of a spin-off series generally revolving on this art style, as seen here:
A big head with small limbs. This is indeed an art style called super-deformed (SD) and is also known as chibi. As said before, it can be used for many reasons, such as to show unusual excitement, unsatisfaction, confusion, etc. The art styles super-deformed and chibi are generally the same thing, and is the style shown in your photo.
Sources: Wikipedia, tvtropes.org.