The phrase "ill-defined notion" is correct and can be used in written English.
You can use it to describe an idea or concept that is unclear, vague, or lacking a specific definition or understanding. Example: "The concept of love is often considered an ill-defined notion, with different people having varying interpretations of its meaning and significance."
Florida v. Riley 488 U.S. 445 (1989), cited by Solove and directly relevant to the UAS secrecy issues, displayed the court's ill-defined notion of infringement.
The ubiquitous, ill-defined notion of "fatigue" may be used as a proxy for other more specific individual- and system-level factors, including limited experience, limited content or patient-specific knowledge, high workload, and inadequate supervision.
Using broad, ill-defined notions like capitalism invites ideological grandstanding and distracts from the hard technical problems.
We cling to ill-defined notions of our uniqueness but robots, for all their limited independence of movement and thought, keep insisting on another question: what makes us so special?
Hence what one sees as increased public displays of affection is merely the inevitable effect of an increasing number of young couples in urban India, who, because of an antiquated legal system with ill-defined notions of "public decency," unfortunately find themselves unable to have safe spaces of their own.
An ill-defined, controversial notion is no basis for coherent policy.In this section What are brands for?
But the historic march represents something far more significant: the growing number of voters unwilling to allow politicians in thrall to ideological obsessions or narrow party interests to use an ill-defined and chimerical notion of the "will of the people" to drive through divisive and potentially catastrophic agendas.
Krauss dismisses this criticism and says that the "nothing" of his critics is some "vague and ill-defined" and "intellectually bankrupt" notion of "nonbeing".
Clearly, without a precise specification of what a concept or conceptual cognition is, the notion of nonconceptuality is equally ill-defined.
Throughout the document, as well as in political discourse and popular parlance, the notion of "Turkishness" is both ill-defined and staunchly defended.
The second problem is that the entire notion of common ancestry is ill-defined, especially in light of lateral genetic transfer.
