The word memorial as defined by the Unger’s bible dictionary means -that by which the memory of any person or thing is preserved. In both the Old and the New Testament we find many occasions for memorials. The feast of the Passover is a memorial of God sparing the firstborn of the Israelites while slaying the firstborn of the Egyptians (Exodus 12:14). The heap of stones left in the bed of the Jordon was a memorial of the Israelites crossing it (Joshua 4:7). The two engraved stones upon the shoulder pieces of the high priest’s ephod were memorial stones for the sons of Israel (Exodus 28:12). Aaron would then bear their names before the LORD on his two shoulders as a memorial.
A memorial was also seen as a record as stated in Exodus 17: 13-14 when Joshua defeated the Amalekite the LORD told Moses, write it as a memorial in a book, and rehearse [it] in the ears of Joshua: for I will utterly put out the remembrance of Amalek from under heaven.
This is also recorded in Malachi 3:16- Then they that feared the LORD spake often one to another: and the LORD hearkened, and heard [it], and a book of remembrance was written before him for them that feared the LORD, and that thought upon his name.
The act of Mary in anointing the feet of Jesus was to be spoken of in “memory of her” – Mat 26:13 Verily I say unto you, Where so ever this gospel shall be preached in the whole world, [there] shall also this, that this woman hath done, be told for a memorial of her.