Object is any entity that participates in some activity within a system. For example, within Banking system, Customer is an object which participates in day to day activity. Since Object Oriented Programming implements the behavior and interaction of real world objects, real world objects should be used as an object in Programming.
Objects should have its own property and behavior. For example, Customer in Banking system may have first name, last name, address and based on activity and account balance you can consider it as Regular customer or Premium Customer, etc.
Bank may have more than one customer and each customer has unique account number. Similar way, in programming when you create customer objects, each will have its own account number and properties like first name, last name, address etc.
Relation between Class and Object :
Class is a blue print which defines the properties and functions of an object.
Object is an instance of Class