An engram might not be an actual thing but if it is, it's a memory-trace – a permanent change in the brain which would account for the existence on memory.
I have lots of great memories and this photo represents many of them - they're some of the flowers from our wedding. They were grown in our garden and delivered to the venue in our campervan to an event shared with friends and family.
Obviously there was cake involved and I even signed a copy of my first novel which was released earlier that year. Oh, and my dress was purple.
What do you think? Do the things we experience physically change our brains in some way?