Identifying Wt Symbol for Piston Assembly Inertia Formula

[Jaguar7555]

Here is the formula in the screenshot figuring piston assembly inertia.
piston assembly inertia = Reciprocating Mass * CRANK RADIUS * W^2*(COS(Wt)+(crank radius/rod length)*COS(2*Wt))
W=angular frequency (crank rotations in 1 second times 6.28)
Wt=unknown
CRANK RADIUS=piston stroke/2

Please identify the Wt (omega t) symbol. thanks

Here's the screenshot:

 

[DrClaude]

Could you please provide the full link?