sidereal period
period is the time required for a celestial body within our solar system to complete one revolution with respect to the fixed stars i.e., as observed from some fixed point outside the system.
sidereal day
one day of sidereal time; the time in which Earth rotates once around its axis, relative to the point of the vernal equinox
sidereal year
time taken by the Earth to orbit the Sun once with respect to the fixed stars