A device in a transformer to change the number of coils used, since the voltage ratio of a transformer is based on the ratio of the number of turns between the primary and secondary coils, changing the number of turns changes the voltage.

A tank truck, gas truck, fuel truck, or tanker truck (United States usage) or tanker (United Kingdom usage), is a motor vehicle designed to carry liquids or gases on roads.

According to the philosopher Piyush Mathur (2017), "Tangibility is the property that a phenomenon exhibits if it has and/or transports mass and/or energy and/or momentum".

Tailings are the materials left over after the process of separating the valuable fraction from the uneconomic fraction of an ore.

Systems theory is the interdisciplinary study of systems, which are cohesive groups of interrelated, interdependent parts that can be natural or human-made.

Systems engineering is an interdisciplinary field of engineering and engineering management that focuses on how to design, integrate, and manage complex systems over their life cycles.

System grounding is required for use in systems like utility distribution systems, telecommunications systems, and in commercial/residential buildings where any significant metal system must be bonded together and referenced to the earth at one point.

A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole.

A fuel that is manufactured as opposed to naturally existing fossil fuels. Synthetic fuels, or commonly known as Synfuel, are made by combining hydrogen, produced from water, and the greenhouse gas CO2.

Synroc, (synthetic rock), is a means of safely storing radioactive waste.

In AC electrical power systems, a synchroscope is a device that indicates the degree to which two systems (generators or power networks) are synchronized with each other.

Time synchronized measurements made up of an angle measurement and a magnitude measurement from a Phasor measurement unit.

A DC-excited synchronous motor, whose shaft is not connected to anything but spins freely.

In an alternating current electric power system, synchronization is the process of matching the frequency of a generator or other source to a running network.

A switching station is a substation without transformers and operating only at a single voltage level.

Switchgear is a switch used to make or break an electrical connection. Switchgear comes in various sizes depending on the voltages of the electrical circuit. Essentially the same as a domestic light switch but for higher voltage applications.

A switched power supply is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently.

Sustainable refurbishment describes working on existing buildings to improve their environmental performance using sustainable methods and materials.

The Sustainable Development Goals are a collection of 17 interlinked global goals designed to be a "blueprint to achieve a better and more sustainable future for all".

The use of energy is considered sustainable if it meets the needs of the present without compromising the needs of future generations.