What is conical pendulum? Find its time period of rotation.

A conical pendulum is a small heavy mass attached with massless, flexible and inextensible string suspended from a rigid support and the mass is a constraint to whirl in a horizontal circle with constant speed. 
Consider a conical pendulum consisting of point heavy mass m attached with massless, flexible and inextensible string of length l.
Let the pendulum be suspended from a rigid support S and the mass be whirled with constant speed v in a horizontal circle of radius r, such that the string makes an angle θ with the vertical. 
                    

The different forces acting on the mass are: 
(i) Weight mg in vertically downward direction. 
(ii) Tension T in the string along AS.
Resolve the components of Tension T, as shown in figure.
The component Tcosθ balances the weight mg of the mass and component T sinθ provides the necessary centripetal force to whirl the mass.  
Thus,