indeterminate form
Technical term in mathematics and logic for an expression whose value is not determined, such as 0/0 or ∞−∞.
This limit is an indeterminate form, so we need to use L'Hôpital's rule.
noun which may take the genitive case particle 'no'
undefined; indefinite; unstructured; amorphous
Describes something lacking a fixed shape, clear definition, or stable structure; can apply to abstract concepts, plans, or physical forms.
The project plan is still undefined, and no concrete schedule has been set.
I kneaded the amorphous clay and made a shape I liked.
無定形 is a near-synonym for the amorphous sense, but 不定形 is more common in mathematical contexts.
不定形 describes something with no fixed shape, the direct opposite of 定型's fixed, standardized form.
Compound of 不 (fu, 'not') + 定 (tei, 'fixed') + 形 (kei, 'form'). The mathematical sense is a calque from English 'indeterminate form'.