Private goods are referred to as rivalrous and excludable by economists. Let me explain what this means in a simple and comprehensive way.
When a good is rivalrous, it means that one person's use or consumption of the good diminishes its availability for others. For example, if you eat an orange, there is now one less orange for someone else to consume. The consumption of the orange by one person reduces the availability of the orange for others.
On the other hand, when a good is excludable, it means that it is possible to prevent someone from using or consuming that good if they do not pay for it. For instance, if you go to a movie theater and buy a ticket, you are allowed entry to watch the movie. However, if you do not buy a ticket, you will be excluded from watching the movie.
Private goods possess both of these characteristics. They are rivalrous because one person's use or consumption of the good reduces its availability for others. For example, if you buy a car, only you can use it at any given time, and someone else cannot simultaneously use it. Private goods are also excludable because it is possible to prevent others from using or consuming the good if they do not pay for it. For instance, if you purchase a book, you have exclusive access to read it unless you choose to share it with someone.
In summary, private goods are referred to as rivalrous and excludable because their consumption diminishes their availability for others, and it is possible to exclude others from using or consuming them if they do not pay for them.