Clarifying Young's Modulus and Stiffness Equations for Cantilever Oscillation

[zeldaspurpose]

Just want clarification on two equations.

So basically, I want to calculate the time period T of the complete oscillation of a cantilever. I use this equation.

Is E equal to young's modulus or is it equal to stiffness? If it is equal to stiffness, can I use this equation to calculate the stiffness?
k =

Thank you in advance. :)

 

[Chestermiller]

What is your definition of the parameter that you call "stiffness?"

 

[zeldaspurpose]

In my case, I think it is the resistance of deflection. However, when I search online that is also the definition for Young Modulus. Yet there's these two different equations which is confusing.