Difference between DYNAMIC_RAM and STATIC_RAM:

RAM ( Random Access Memory )

first we will get cleat with word RANDOM means in RAM- IT means that you can access any address of RAM randomly .(ie., you can go to particular address directly )
There is another type of called SERIAL ACCESS MEMORY - In this you should go to a particular address serially . (example - If address is '10' and now you are at '4', you cant goto '10' directly, you should go serially like 5,6,7,8,9 and then to 10 .

Difference:

Memory means storage of bits, right! .

In DYNAMIC_RAM bits are stored in the form of charge in the capacitor .
As capacitor discharges it should be refreshed frequently to store the value correctly.
so there should be one unit which refreshes every memory cell frequently, thats why dynamic_RAMs are slow .

In static_RAM the bit is stored in a Flip_Flop.
one flip flop needs 6 to 8 transistors to store a bit, so static_RAMs are costly compared to Dynamic_RAMs which use only one transistor and a capacitor to store a bit.

static_RAMs are faster compared with Dynamic_RAMs