People perceive things differently based on past experiences, and because everyone assigns a different meaning to what they are perceiving. Perceptions are also subject to change.
Perception can pertain to the direct awareness of physical things. It relies on the senses to tell people what they are seeing, feeling, tasting or listening to. The second meaning of perception refers to the way something is interpreted. This can translate into the way a person feels about a particular piece of music, or how they feel about something they have read.
Almost everything humans do and see on a day-to-day basis can be perceived, and will always be perceived differently by different people.