Electrum uses hiearchial determistic(HD) seeds to generate addresses. Using the seed, the client can generate a master private key which can generate a practically unlimited number of addresses. The default behavior of Electrum is to generate addresses till they find an àddress with Bitcoins and generate an additional 10 addresses after that point. Judging by that, you likely had 16 transactions using your wallet.
I don't completely understand 
but thanks anyway. One more question, I exported those addresses, will it use these addresses only or it can generate new ones again and again, I want the same address.