Correct Answer  Option 2 : Static velocity error coefficient
Explanation:
Type
It is defined as the number of poles at the origin in the openloop transfer function.
Error: It is the deviation of output from the input.
 If the actual output of an openloop system during the steadystate deviates from the reference input then the system is said to have a steadystate error.
 It is the index of accuracy of the control system.
 It is also called a ‘static error’.
Steadystate error is defined as:
\({e_{ss}} = \mathop {\lim }\limits_{t \to \infty } e\left( t \right) = \mathop {\lim }\limits_{s \to 0} sE\left( s \right)\)
Error constant and ess
The below table gives all information about the ess and error constant.
Type of input

Input: r(t)

ess

Error constant

Step

A.u(t)

\(\frac{A}{{1 + {k_p}}}\)

Position error constant
\({k_p} = \mathop {\lim }\limits_{s \to 0} G\left( s \right)\)

Ramp

A.t.u(t)

\(\frac{A}{{{k_v}}}\)

Velocity error constant
\({k_v} = \mathop {\lim }\limits_{s \to 0} sG\left( s \right)\)

Parabolic

A.u(t).t2/2

\(\frac{A}{{{k_a}}}\)

Acceleration error constant
\({k_a} = \mathop {\lim }\limits_{s \to 0} {s^2}G\left( s \right)\)

Hence Static velocity error coefficient is associated with the Unit Ramp function.