Class - A representation of something with the use of properties and functions that might do something with these properties. Example class dog can have a collar and have a renewCollar() function.
Object - The class is instantiated inside a program and exists as an object in the memory, the heap.
Overloading - Providing a different implementation for the same method based on the inputs received. Ex renewCollar() and renewCollar(License li)
Overriding - Providing a different implementation for the same method in a subclass. Ex: Labrador class extends Dog class and both have the renewCollar() method with same signature. renewCollar() works differently with Labrador than with a Dog.
Polymorphism - Stuff like inheritance, overriding represent polymorphism.
difference between thread and process - A thread is like a part of a process. A process can spawn many many threads. When you start a program you start a process. That process in turn may use multiple threads to execute code. Each thread is given a time slice of the processor to execute.
You should google first before you ask here.