For a baby, that might mean knowing things like what applesauce looks like or that the stove could be hot. As he grows, his semantic memory will expand to include things like a green light means go, or a knock on the door signals that there are visitors.
As recently as a decade ago, researchers assumed that an infant's brain was too undeveloped to remember much more than these simple motor responses and associations for the first year of life. However, current memory studies reveal that babies are able to remember relatively complex pieces of information at a young age. What's more, your baby's memories can last for a long time, especially if you help him to strengthen them.