Every time you make transaction in Electrum wallet is create "change address" and on that address is change what left when you send
BTC.Let's say you have 0.2
BTC on some address and want to send 0.1
BTC,wallet use total amount from that address in a way that send 0.1 to address you chose and other 0.1 minus fee is allocated to that change address you see.
This is very good for your privacy because on this way it is hard to somebody to know how much
BTC you have and where you send them.There is option to disable using of change address in Preferences/Transaction,but it is recommended to not disable this option just because of user privacy.