Symbols:T

Set

 * $T$

Used to denote a general set, often in conjunction with $S$ when two such sets is under discussion.

Algebraic Substructure

 * $T$

Used to denote a general algebraic substructure, of the algebraic structure $S$, in particular a subsemigroup.

In this context, frequently seen in the compound symbol $\struct {T, \circ}$ where $\circ$ represents an arbitrary binary operation.

Topological Space

 * $T = \struct {S, \tau}$

Frequently used, and conventionally in many texts, to denote a general topological space.

General Binary Operation

 * $\intercal$

Used in to denote an arbitrary binary operation in a general algebraic structure.

It is given the name truc, pronounced trook, French for trick or technique.

himself suggests that truc could be translated as thingummyjig, but this is linguistically unsupported.