“The morrow after the Sabbath” means the day following the Sabbath, understood in the supplied material as the first day of the week. It designated the time for formal offerings of first-fruits.
On this day Israel presented the first wave-sheaf, and fifty days later the wave-loaves were offered at the Feast of Weeks.
The recognition of a day after the Sabbath during festival periods is presented as having a counterpart in later practice concerning Easter Sunday and the following days.