1. What is meant by i3, i5, i7, i9?
It refers to the purpose for which you are going to use it. For normal daily life purpose you should go with i3. If you do video editing more than a normal editing then you should go with i5. And if you want high end gaming peformance then you should go with i9.

2. What is meant by dual core, quad core, octa core etc..?
These terms refers to the numbers of cores a processor is having inside it. Dual meant 2, quad meant 4, octa meant 8....

3. What is P core and E core in processor?
P stands for performance and E stands for efficiency. Cores are nowdays being divided into P core and E core separately on the chip. For normal running tasks E cores will be used (P cores will be off during this), and for tasks that requires high performance P cores will start being used. Suppose a CPU is Octa core with 6E cores and 2P cores. Meant on this you can get more efficiency and less performance as compared to a 2E cores and 6P cores processor.

4. What is Gigahertz (GHz)?
The term Hertz means the number of times current is turned on and off in 1 second of time. So, 1 GHz meant current will go off and on 1 Million of times in a secoond. This term is also known as clock speed. More the value of GHz higher the performance you will get.

5. What is overclocking?
It is a method to increase the clock speed (GHz) of your CPU without chaning it. It is done by providing more power supply to it then required. You can increase clock spped from 3.5 GHz to 4GHz. The letter K in its SKU name indicates whether you can overclock a CPU or not.

6. What is meant by generation of CPU?
The term generation means which technology has been used in making that CPU. Every year intel releases a new generation in each i3, i5, i7... In each new generation launched size of cores/transistors goes smaller and smaller. And smaller the size of transistor better the performance you get.

7. What is Hyperthreading?
It is a method (hack) to virtually increase the number of cores a CPU is having without actually changing the CPU. Well, you do not need to do so or enable it by yourself, it comes in built for different kind of CPUs. You can check for its existence by counting the number of threads to the number of cores, whether it is double or not.

8. What is integreted and discrette graphics processor?
Integreted refers to the GPU that is in built provided on the CPU and uses lesser power than discrette one to procces normal graphics running on the system. Discrette refers to the GPU that requires a separate Graphics card to process graphics running on the system. A discrette GPU gives more performance to the system but it consumes more power. SKUs with letter 'F' in it meant that requires discrette graphics card to proccess even a low end-video games like GTA vice city. While the letter 'G' meant integrated GPU.

9. What do letters Y, U, P, H, HK, HX meant?
These letters in the SKUs provides  information regarding the power  consumption/battery backup and performance it will provide. You can refer to the following table for better understanding regarding whihc one is better for your requirement. These SKUs can only be seen on CPU that are designed for Laptops (for desktops refer to intel official site).