alb sunday

from The Century Dictionary.

• noun The first Sunday after Easter: so called because on that day those who had been baptized on Easter eve wore their white robes for the last time. Also called Low Sunday.

from the GNU version of the Collaborative International Dictionary of English.

• (Eccl.) The first Sunday after Easter Sunday, properly Albless Sunday, because in the early church those who had been baptized on Easter eve laid aside on the following Saturday their white albs which had been put on after baptism.