addresses are generated according to a sequence. each address has an index number for example 0,1,2 etc. electrum generates new addresses such that if you were to arrange your addresses in ascending order of index number you would have at least 20 unused receive addresses at the end of your wallet. that number 20 is called the gap limit. the gap limit for change addresses is 6 and functions similarly.
for example you start a new wallet and you have 20 receive and 6 change addresses. you use address with index 18 (19th in the list) to receive bitcoin. electrum will generate 19 new addresses starting with index 20 so now you have 39 receive addresses and 6 change ones.
Ok now it started to make sense. Thank you very much.
All those days I was wondering what if I use all these 20 addresses? Finally it gives me the answer that I can use as many address as I want from a wallet that was generated using Electrum.
+2 merit for you bud
Cheers :-)