The phrase "are further defined as" is correct and usable in written English.
It can be used when you want to clarify or elaborate on a term or concept that has already been introduced.
Example: "In this document, the terms used in the context of data privacy are further defined as follows: personal data, processing, and consent."
Alternatives: "are additionally described as" or "are elaborated on as".
These latter-day ley lines are further defined as "rods of force" that are active in this city.
Farm profits are further defined as the value of farm production minus the input costs.
Therefore, the speed bounds vmin and vmax, denoting the lower and upper limit of velocity respectively, are introduced, where vmin and vmax are further defined as vmin = μ − 3σ, vmax = μ + 3σ.
"Medical products" are further defined as a "drug, device, or biological product".
Negative actions are further defined as when someone (the "perpetrator") intentionally inflicts, or attempts to inflict, injury or discomfort upon another (the "victim").
Tibial torsion is a well known anatomical feature of the tibia; it was first described in the early 1900s and was further defined as soon as CT investigations became available (Le Damany 1909, Jakob et al. 1980, Takai et al. 1985).
A natural fibre may be further defined as an agglomeration of cells in which the diameter is negligible in comparison with the length.
In theology, the soul is further defined as that part of the individual which partakes of divinity and often is considered to survive the death of the body.
If I remember correctly, he boils it down to the habit of living a virtuous life, which is further defined as being mindful of choosing the mean between extremes (i.e., to be courageous is to be neither foolhardy nor a coward).
A machine may be further defined as a device consisting of two or more resistant, relatively constrained parts that may serve to transmit and modify force and motion in order to do work.
It can be further defined as that form of fermentation, characteristic of cells in general, in which the six-carbon sugar glucose is broken down into two molecules of the three-carbon organic acid, pyruvic acid (the nonionized form of pyruvate), coupled with the transfer of chemical energy to the synthesis of adenosine triphosphate (ATP).
