"a system is required that transforms the engine's output so that it can supply high torque at low speeds, but also operate at highway speeds with the motor still operating within its limits. Transmissions perform this transformation."

https://en.wikipedia.org/wiki/Propulsion_transmission#Automo...

I think it's simply referring to the transmission operation, and then providing the definition.

Two points at issue here:
1) The expression I am most familiar with in this context is “relación de transmisión” rather than “desarrollo de transmisión”.
2) If I am right, “desarrollo de (la) transmisión is the same as “relación de (la) transmisión”, which translates as “gear ratio” into English. This is the key point here, and I must admit I am not absolutely sure of this. But I think when the author refers to “desarrollo de transmisión”, they mean “relación de transmisión”.

The definition you quote:
https://www.tecnologia-automovil.com/articulos/tecnologias-l...
TIPOS DE DESARROLLOS Y DE RELACIÓN DE TRANSMISIÓN EN CAJA DE CAMBIOS
(…)
Concepto de desarrollos de transmisión
Desarrollo de transmisión es la relación entre la velocidad del automóvil (km/h) y el régimen de giro del motor (RPM) en cada una de las marchas de la caja de cambios, en este caso de seis marchas.

https://www.merriam-webster.com/dictionary/gear ratio
gear ratio
noun
Definition of gear ratio
: the ratio of the angular speed of the initial or driving member of a gear train or equivalent mechanism to that of the final or driven member specifically: the number of engine revolutions per revolution of the rear wheels of an automobile.

In this link, both terms (“desarrollo” and “relación”) appear as synonyms:
https://e-archivo.uc3m.es/bitstream/handle/10016/24303/PFC_J...
Diseño e implementación del sistema mecánico, propulsión eléctrica y electrónica de control de un propulsión eléctrica y electrónica de control de un longboard eléctrico
(…)
4.1.3 Transmisión mecánica.
(…)
Con estas dos especificaciones, es posible calcular y seleccionar las poleas correspondientes, es decir, el desarrollo o relación de transmisión, para que se cumpla la especificación de velocidad.

This is also a very interesting link (and trilingual: English, Spanish and Basque):
https://www.fsbizkaia.com/single-post/the-reduction-gearbox


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Note added at 3 days 23 hrs (2022-05-31 12:09:18 GMT)
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Another interesting link for those still sceptical about the link between RPM of engine and RPM of wheel.
https://www.team-bhp.com/forum/technical-stuff/85325-underst...
(...)
In automobile context, Gear Ratios are the ratios of driving gears with respect to the crank shaft gear. In other words, these are the ratios of engine RPM to the RPM of the wheel. For example, if first gear ratio if 4.0, then the engine RPM will be 4 times the RPM of the wheel or axle, when you are in first gear.