Own-price refers to the price of the item you are analyzing. If you analyze car demand, own-price refers to the price of the car.
Economists use the term to distinguish it from the price of related goods, namely substitute and complementary products.
If the own-price changes, it causes the quantity to change, but it moves along the curve, whether it is the demand curve or the supply curve.
While changes in prices of related goods cause quantities to change and curves to shift, right or left.
Economists use the term “change in quantity demanded” to refer to changes in quantity due to changes in its own price. Too, they use the term “change in demand” to indicate changes in quantity due to factors other than own-price.
The demand curve below might help you to understand what I mean.
