Dialectical Behavior Therapy's Biosocial Theory - Social Environment Validates Patients' Maladaptive Behavior - As Defined By Who/What? In Wikipedia's article about DBT, in the overview section it says:

In DBT's biosocial theory of BPD, clients have a biological predisposition for emotional dysregulation, and their social environment validates maladaptive behavior.

According to the theory, &quot;maladaptive behavior&quot; - as defined by who/what - the patients' view of their social environments' various norms or the scientific-concesus of maladaptive behaviors (or something else)?
In some cases, patients' environments' view of what reoccuring behavior in the patient is maladaptive, there no agreement between that and the scientific concensus - that's why it's important for me to know which one the theory refers to.
I'm assuming the article refers to the scientific concesus definition of &quot;maladaptive behavior&quot; but I want to make sure.
Just as a point of note, you said you are quoting from Wikipedia, but it is actually WikiWand you are linking to.
The article cited Little, et al. (2018) which states that (emphasis mine):

DBT is based on a biosocial theory of BPD, which posits that the core difficulties seen in this diagnosis stem from the relationship between two factors. Firstly, those diagnosed have a biological dysfunction of the emotion regulation system; and secondly, their environment is invalidating, inhibiting the use of positive behavioural skills and reinforcing the use of less helpful ones (Feigenbaum, 2007; Linehan &amp; Kehrer, 1993)

Feigenbaum (2007) states (again, emphasis mine):

The DBT model assumes that: (i) individuals with BPD lack key interpersonal and self-regulation skills, and (ii) personal and environmental factors may frequently block and/or inhibit the use of behavioural skills or reinforce maladaptive actions.

In psychology, when evaluating the client's environment, you need to look at things from the client's viewpoint, and reading those papers, it highlights that the term maladaptive actions or maladaptive behaviours refers to the consensus that they are as Anestis, et al. (2007) points out:

actions for which cost outweighs benefit [and] is a defining feature of a host of psychological disorders, including depression, eating disorders, and substance abuse disorders (Bornovalova, Lejuez, Daughters, Rosenthal, &amp; Lynch, 2005; Claes, Vandereycken, &amp; Vertommen, 2005; Fischer, Anderson, &amp; Smith, 2004; Joiner, Metalsky, Katz, &amp; Beach, 1999; Keel &amp; Mitchell, 1997)

The client believes that their environment backs up their notion that their behaviours are justified and therefore blocks any move towards more helpful behaviours.
References
Anestis, M. D., Selby, E. A., &amp; Joiner, T. E. (2007). The role of urgency in maladaptive behaviors. Behaviour Research and Therapy, 45(12), 3018–3029. https://doi.org/10.1016/j.brat.2007.08.012
Feigenbaum, J. (2007). Dialectical behaviour therapy: An increasing evidence base. Journal of Mental Health, 16(1), 51-68. https://doi.org/10.1080/09638230601182094
Linehan, M. M., &amp; Kehrer, C. A. (1993). Borderline personality disorder. In D. H. Barlow (Ed.), Clinical handbook of psychological disorders (pp. 396–441). New York, NY: The Guilford Press.
Little, H., Tickle, A., &amp; das Nair, R. (2018). Process and impact of dialectical behaviour therapy: A systematic review of perceptions of clients with a diagnosis of borderline personality disorder. Psychology and Psychotherapy: Theory, Research and Practice, 91(3), 278-301. https://doi.org/10.1111/papt.12156