a memorial: something set up or kept so that a person, event, or obligation is not forgotten
This word points to whatever holds something in remembrance. It grows out of the everyday verb "to remember," and it names the concrete result of remembering: a reminder you can see, touch, observe, or read.
In Israel's worship the word takes on real weight, and it faces two directions. Some memorials face the people: the yearly Passover, the standing stones taken from the Jordan, a festival of trumpet blasts, all set up so that a later generation asks what they mean and hears the story again. Others face God: the names of the twelve tribes carried on the high priest's shoulders and over his heart, the blowing of trumpets, the silver collected at the census, each called a memorial "before the LORD," a way of keeping Israel in God's attention.
The same word can also be a written record, whether the palace book of daily events read to a sleepless king in Esther or the book of remembrance in Malachi where the names of the faithful are entered. At its thinnest it is simply memory itself, as in Ecclesiastes, where in the end the wise and the fool alike are forgotten. Across the whole range one thread holds: it is a guard against forgetting.